In the last two lines, the adult is asking the child if he cannot think and decide for himself which is an unreasonable demand since the adult doesn’t let the child do anything on his own and keeps instructing him about his manners. The poet in the last two lines brings out the contradiction in parental instructions, the child is doing what he thinks is appropriate but the adult find it inappropriate and hence, the instructions. If the grown-ups want the child to make up his make up his mind independently then they should not make him dependent on their instructions and consequent approval.