system
Given the following post, respond as if you're commenting on Reddit:
human
[Pokemon] What's going on with the Kangaskhan baby? Is it even a baby or just an anomaly?

There's no evolution that involves the baby growing up and leaving. In fact, we can breed kangaskhan, and they come out of the egg already with a baby. 

Now, this may be game mechanics, but that doesn't add up. They didn't adjust that when they introduced baby pokemon forms in gen 2. Lots of pokemon got baby forms, but no explanation was given for the kangaroo. 

What's going on canonically with the baby in its pouch?
gpt
Baby Kangaskhan turn into Cubones if their mother dies.

Cubone -> Marowak -> Kangaskhan 

Evidence: 

* Cubone skull shape similar to Kangaskhan 

* Very similar physiology 

* Both overtly Australian (bone-merang, kangaroo)

* In Pokemon Sun and Moon, Cubones' "Call for Help" can summon a Cubone or a Kangaskhan. Most Pokemon only call others from their own evolutionary line.

* The only real reference to "mothers" in original Pokemon were Cubones and Kangaskhan... and the dead Marowak in Lavender Town. 

* Kangaskhan likely had an evolutionary line in the original game. If you evolve M', it turns into a Kangaskhan.