Why do we consider children non-sexual beings?

Let me preface this by saying I am in no way implying that I think it’s okay for adults to view children sexually or to have sex with them.

Daloon’s question about young girls’ sexual attributes raised this question in my mind. As a society, we are squeamish about admitting that children have sexual thoughts and feelings. We protect children from hearing about sexual acts, and we forbid children from engaging in them.

Why? What are the benefits of reserving sex for adults? What are the negative consequences of allowing children access to sex and sexuality?