Why are kids disobedient? I think the reasons are complex and manyfold, and varying with age.
Humans take a long time to develop, after 9 months they're mostly able to survive without an umbilical cord, but it takes another 25 years or so before we really consider their brains to have become “adult”. (The rental car industry figured out they shouldn't trust under-25 year-olds.)
During that entire time children go through many stages of understanding and learning. Puberty brings them a greater capacity to empathize with other people, and at a very young age (the first couple years) they lack much capacity to empathize with others at all. (I'm not an expert on any of these topics so my estimates of ages and abilities should be understood to have healthy margins of error; also no two children are alike, there will be variation for what age exactly a child really grasps what concept.)
Before puberty children will typically have a certain kind of trust, in particular for their parents. Evolutionarily this is important because offspring that don't listen to their parents when they're told “don't get too close to the edge” or “don't eat that” fall and die or get poisoned and die—evolutionarily we are selected to listen to our parents, to a degree. Even so, there is a tradeoff, between an organism that is confined to do everything it is told, and the benefits of exploring the world and going against the received dogma. Exactly how children “rank” in this tradeoff has a great deal of variation, as a child I was very “conservative”—nervous to do anything other than what I was told, but my best friend was adventurous, always “breaking the rules”.
As children go through puberty this tends to shift towards the more adventurous side. (Hence the rebellious teenager.) There is a stronger urge to explore, to disregard received wisdom, try new things. In nature this should have helped younger members venture out and learn new things, possibly at times splitting off into new groups (if a group were reaching the carrying capacity of the food supply in that vicinity), discovering new resources, and so on.
The lessons learned early in childhood might reasonably provide some “cushioning” to reduce the magnitude of the risks they take in adolescence. (How many times did I stab myself with flathead screwdrivers as a child while trying to pry something apart? Eventually I learned not to do that!) But obviously the risks adolescence take are often still great (as motor vehicle fatalities, and drug use, indicate).
These are just my thoughts on the subject, I'm sure someone who has studied human development in greater detail would have plenty of criticisms, and many fascinating insights, to contribute.