Most people would probably concede in some way or another that there are certain laws that have been universally accepted based on their need in order to maintain a civilization. On this general idea, they would be correct in believing that there are universal moral laws that most people obey because they realize that they are necessary for order and well-being, but unfortunately many of them are wrong about which laws are truly necessary to this end. In my view, many of our everyday decisions and actions are done within the ordered framework of a sort of "anarchy" in which each individual, through their own free choice, choose to obey certain moral laws out of their fundamental self-interest of survival and well-being, and also often out of an interest for the survival and well-being of others. These "anarchic" laws are heavily ingrained into the modern human psyche. They are the result of years of trial and error, and are quite instinctive.
Many of the very same people who concede, in short, that there must be universal ethical laws simultaneously sniff at the implication that these universal ethical laws are "natural". They sniff even more at the term "human nature". But what other rational way is there to arrive at the universal ethical law against murder than on the basis that it is contrary to what is objectively best for the murder victim's nature (I.E. staying alive) as a living being and as a species? The reason why the law against murder is virtually universally accepted is because people recognize that murder violates their nature, the natural path of survival, the natural state of living. By our natures, we need to continue breathing in order to survive. Murder violates this. The law against murder is natural because it is in protection of our natural ownership over our own bodies and ability to keep living with those bodies. It is in accordance with man's nature and within their interest to continue living, and this is the simple basis by which I accept the prohibition of murder and other things that are determental to living (such as assault and torture).
One may ask, what exactly is the nature of a human being? Well, the simple answer to this question is the same answer to the question "what is the nature of a living being"? To survive and reproduce. However, different species are equipped in different ways with which they can use to help obtain these ends, and this means that humans as a species are equipped with specific physical and mental tools by which they can use to survive and reproduce. But what is truly distinguishing about human beings is that they have the capability to transcend their basic instinctual natures (to make a bold and concious effort to abtain from following their instincts, such as the free choice to not live anymore, as in the act of suicide) - it is an instrinic fact of human nature that we possess the ability to freely choose the course towards our ends, and we have the ability to create other ends that we regaurd as equally important, ends beyond mere subsistance that we define as well-being or happiness. Mankind has the natural tools by which to create artificial tools that are used for purposes that no other animal can persue. In short, mankind has the special gift of being able to either keep the "lizard brain" constantly in a non-dominant mode, or for particularly talented individuals, turn it off and on at will.
On the other hand, others may ask some more contentious questions: what is the nature of a fetus, and is it the same as the nature of a born child? What is the nature of child, and is it the same as the nature of an adult? What are the rights of these beings in these different stages of life? When does life actually begin? Something decently resembling the actual answers to these questions can be found if one looks hard enough and thinks enough, but not in the dens of popular culture. The most controversial of these questions, of course, is the question of the rights of unborn children.
There are some who regaurd fetuses as being subject to the natural laws of human survival (and the rights they imply) as much as a born man. Essentially, the arguement of these people is that an unborn child, in a fetal state, is subject to the human right to life. This view comes most frequently from conservatives, although when one thinks about it, they are buying into a conception that quite "liberally" applies and expands rights to unborn children. It is strange that the very same people known most for preaching about the virtues of tough parenting (and thus, in this sense, a restriction on the rights of children) tend to adopt a view of fetuses granting more rights then their prefered parenting model may grant to born children. To these people, abortion constitutes murder because the fetus is subjected to the same standards that grown adults are subjected to.
If I were to actually accept their application of the standards to fetuses, which I do not, I can put myself in the mental place necessary to see why they consider abortion to be murder. But I quite strongly disagree with them on what the nature of the fetus is. I do not accept their conception of pre-birth rights or their definition of a human being. Life itself indeed does begin when the sperm fertilizes the egg - it is at this point for all intents and purposes, a simple celled form of life. But it is not a "human being". A "human being" is someone who has been born already, after that first simple-celled form of life becomes so complex and multi-celled as to form an actual species. The simple-celled phase of its life has no real conciousness or will, and therefore cannot be considered a sentient being, let a lone a human being. It is life, but it is not concious or human life.
Therefore, you cannot apply "human rights" to something that is not fully formed yet into a "human being". You can, however, call it "life" all you like. I do not consider the nature of a fetus to be the same as a born child, and I will rather controversially point out what I consider to be obvious: a fetus's nature is to be a parasite on its mothers supply of nutrients. Once it is born, it developes a different nature and is no longer a biological parasite. Once it is a born human being, it's mode of survival changes from one that is biologically dependant on others to one that is biologically independant of others but of course is still dependant on its parents for survival in economic ways.
A note on "growing up": A new-born baby has almost nothing but instinct, because they have no experience to guide them but their genes. In the process of experience, of growing up, they then form what we call beliefs. It is possible to indoctrinate a child with a particular belief from an early age, but no child is actually born with a belief. What is amazing and special about human beings is we are capable of supressing primal instinct in favor of "higher" things such as justice or kindness, and in the process of growing up we learn how to do this through experience. "Growing up" is essentially the process by which we learn to overcome our instincts in order to act in a way that creates the best utility for human well-being and that subjective thing that we call "happiness". What I am saying should not be mistaken for the view that all of our instincts are inherently bad and therefore should be brutally supressed (I contest this view strongly), I am just emphasizing the human characteristic of being able to transcend them.
It is a scientific fact that humans are among the most defenseless of newborns, and therefore we are essentially required to function like parasites on our parents until we reach adulthood (with the acception of very rare genuises and idiot savants who have managed to be independant at surprisingly early ages). I would put forth that the process of growing up, and thus developing full legal rights, is where that parasitism is slowly siphoned off as the individuals gains more control and independance over themselves physically, mentally and eventually financially. Exactly where the cut-off point is may be hard to determine. Since each individual is different, there will invariably be a certain diversity (and thus, inequality) as to when people truly "muture" in the physical and mental sense (which is why I have a problem with many standardized age limits for certain things).
A child has legal rights to the extent that they are actually capable of expressing them (you can't have a right that you are unable to express), and within the context (and confines) of the "stewartship" role of the parent. It is the role of the parents to help the child gain their rights in the process of growing up, while tending to those areas where the child is not yet capable of expressing the responsibilities necessary to realize the right. The stewartship role of the parent diminishes in direct proportion to how fast the individual child gains self-control. At the point when full-self control is achieved, I consider this to be when one is truly a "legal adult" (but, as I stressed above, there is no uniformity as to when this occurs). A right exists in direct proportion to the individual's ability to control themselves in order to express it in mental or physical action.
In short, it is a result of what some may call "free will", and it is my contention that one is born without full free will (it exists to an extent, but instinct blocks it from full fruition in a child - the process of the child learning how to supress his instincts is how he forms his free will), but slowly develops it fully along with their rights. The rights of the child, and eventual adult, are thus determined as a natural outcome of the process of "growing up". This framework for rights helps deal with the heavily debated issue of "children's rights" in my opinion, because it is self-actualizing (and thus, natural) on the basis of the individual's actual developement as a human being.