Tit for tat and kids

I have been re-reading Robert Axelrod's The Evolution of Cooperation, in which he makes the case for a tit-for-tat response when situations resembling the prisoner's dilemma are repeatedly played. It struck me that children do not play tit-for-tat in interacting with their parents. Instead they are much more likely to test to see if the parents will retaliate, or perhaps they test to see if parents will play a tit-for-tat strategy. In any case, they violate the rule that one should not be the first to defect. And parents often do not retaliate--they often let themselves be exploited. I suspect that there is an explanation in evolutionary biology.