Could you think children's behavior is determined by genetics or the environment?

Both. Clearly a combination of both.Research has proven that nature and nurture are both influences.Thus good role modeling and mentoring are always important.
Yes & Yes. In the . Transactional Theory of Development , the ongoing interaction of an organism, a baby or child with a certain genetic & biological "set-up" , with its environment, parents, other family members & community members who also have genetic & biological " set-ups", determines the child's trajectory of development in the areas of cognition, learning, adaptive skills, social interaction & behavior. .