There's good evolutionary reasons for babies to not possess a copy of the parents brains. It allows for much better adaptation to the current surroundings, and thus better survival of the species.

so, mitosis?

They would never survive urban life given their susceptability to disease

Is it safe to assume that fission in a complex organism would actually transfer learning?

I'm not confident enough in my grasp of it to say either way. That being said, the geek in me that writes fiction can see the brain duplication ending up with two newborns, or two individuals with bits and pieces of the established pathways of the parent.

We use fission+fusion! We randomly divide our genome, providing the information we have accumulate over Eons, then fuse with another to combine our knowledge. Family group animals are weird because we need to perform additional learning, vs most other animals that run mostly off instinct.

Splits off all the bad. Gets an evil twin.

I mean sometimes you have to let go of things too right?