I believe that this line has a literal and figurative meaning to it. The literal meaning would be that What your child does and what a child does is what is in there world and what they would live on from that world. Meaning that if your child is in a world of violence that the child will exhibit the violence and there fore lives on it, or in it.
The figurative meaning would be your child lives on certain needs, they have the physical which is obvious, food, water, shelter, and then they have the mental needs which is what i believe this line is referring to. The mental needs would be that they need comfort, love, compassion. So what your child does, is what they need in life. If your child is acting in anger and aggression, they need compassion to live on.