At that age, kids are absorbing stuff from their parents still because they haven't yet realized that their parents aren't cool.

I wonder if that's what keeps the whole thing at least somewhat coherent. While a generation of teenagers figures out how they will talk, the younger generation absorbs words and phrases from both their immediate seniors as well as their parents' generation, resulting in a base that's still close to where their parents are. Maybe without that, we'd have entire new languages every few generations.

Hmm that might even be the mechanism that causes fashion trends to repeat on a 20-30 year cycle.