@SuperSajanBonnie But Charlotte Emily died first then Fredbear killed Crying Child/Evan/ then William murdered 5 children and after 5 missining children Elizabeth is killed by Circus Baby.

There is not a definite answer. The reason why he did it is up to debate.

I’m pretty sure it was for revenge or jealousy in Charlie’s case but after that I pretty sure Willam just liked it (or maybe he was just insane who knows nothings confirmed)

I personally believe that William did it out of spite and grief after losing his children (and probably disowning Michael, losing his wife, and other things). (And/or) So he could make others feel his rage and pain. The same could be about when he killed Charlie, but we're not too sure about that one.

After the Missing Children incident, it could be seen that William, by this time, could have discovered Remanety or however it's spelled. Maybe he did another murder because of it, so he could experiment with it.

Or it could just be the same reason as previously stated.

That's my theory, however.

Thx guys! Although I like Kennedy's theory the best. :)

Thanks

Eh, sorta agree.

@John write

Ok, first of all, it's a mystery of whether Afton is either a pure evil or broken villain. We don't know when he killed Charlotte, whether it was before Elizabeth and Evan's deaths. That's the big question. Also Henry referring to William as "old friend" is basically alluding to the fact that Henry and William were formerly friends, but later turned enemies when Henry realized that William was the main culprit responsible for his daughter's death as well as the rest of the tragic events that occurred around Fazbear Entertainment and Afton Robotics LLC.

I'll give you a speculation warning if you keep bringing up your own facts that don't tie in with the lore correctly, so please, cut it out.