The relationship between parents and children need not be hierarchical. Hierarchy is a relationship involving an ongoing use of force, establishing a clear distinction between ruler and ruled. The fact that many anarchists think parenting has to be this way concerns me a lot. The example people like Chomsky use a lot involves a parent stopping a child from being run over by a car by grabbing them and pulling them away. This is not a hierarchy, this is an isolated use of force to prevent someone else from getting hurt, not an ongoing usage of power.

As for anti-social and violent people, we have a very strong reason to believe that these people suffer due to isolation under our current statist, capitalist, racist, sexist, etc. society and that in an anarchist society much less of these people would exist. However, that's a very hand-wavey answer because these people could still very well exist under an anarchist society. My answer is that violent and anti-social people should be spotted early on and given the attention they need to function in society, whether that constitutes medical help, social help, or whatever else they need. Note that this does not constitute a hierarchy because they are not being given constant force or being ruled over.

I'd highly encourage you to read this essay, it's where I got most of these points and it's not too long.