Is it okay for children to have sex? Why or why not?

I do not care who, how old, what gender, what ethnicity, what sexuality, or what zodiac sign you are. Anyone may be allowed to have sex with whomever they want to as long as All Individuals involved:
a) Consent to any and all actions they partake in
b) Know what they are doing
c) Understand what they are doing
d) Know the consequences of such actions

Yes, it is possible for children to meet all the above requirements. Yes, it is possible for adults to meet all the above requirements.
Yes, it is possible for children to not meet one, multiple, or all of the above requirements. Yes, it is possible for adults to not meet one, multiple, or all of the above requirements.

I also always suggest(even though it is not required for having okay, consensual sex) the 3C Rule. It will lead to a fun, comfortable, and free time.
Cleanliness, Consent, Compassion
Cleanliness- know and understand consequences of STIs, STDs, etc—; Understand and know about contraceptives and protection and how to use them!
Consent-Do not rape anyone. Also, keep within the comfort zones of participating parties.
Compassion- It would really help if all individuals actually wanted to be partaking in the sexual activities. They may consent—but are they actually into it? wanting it?