And then a not so nice subject, happening mostly in the wild, but certainly in zoos too. Luckily they can prevent it in zoos, but that didn't always happen.
Infant murder is the other term for it. It happens with a lot of wild animals, like lions, but also with gorillas. When in the wild a (old) silverback is chased away by a younger one or the silverback dies and a new male one takes over the group, this new (future) silverback will kill all the young (still suckling) kids. The reason is that only then he can impregnate the females, because their cycle starts again. Only when a female doesn't have kids drinking anymore, she can get pregnant again. It's important for a (new) silverback to spread his genes.
Like mentioned in the begin, it can be prevented in zoos. But it did go wrong in the past. It's always difficult to find a new zoo for a young gorilla when his dad (suddenly) dies. Depending on the age of that kid, the mom also has to move. Then the same thing can happen in the new zoo. The silverback from that zoo can also kill that kid so he can impregnate his/her mother. Too be honest, because of the cruelty of this subject, I forgot all the cases in detail. There's only one recent incident I remember.
That's in Givskud, Denmark. In July 2015 silverback Samson suddenly died at the age of 43. His older son Kipenzi, was behind the scenes. At one point they decided to put him in the group as the new leader. Since his mom wasn't living anymore, that was possible. In that group were 3 females; 2 with younger kids (he's the half-brother of both these kids). The female without and female with the oldest kid wanted to mate with him; the female with the youngest kid didn't; her cycle was still absent. For 4 weeks there was nothing wrong and the zoo hoped that nothing would happen (maybe that Kipenzi would realize this was his half-brother??). But after these weeks he still killed his half-brother No one saw that coming because for weeks all was fine. I guess they learned a valuable lesson from it.