Save Game leave to main menu, no need to restart game. go to WW settings and look for sex triggers for animations, you will find things like height check for animations. adding post puberty is necessary but it complicates things because the teen now enters the late high school stage status (they will be stuck where (they were previously though). check if the original household doesn't have some other children, if not cheat menu and remove trait caregiver and save the game, leave to main menu or exit gave (preferred) check their JOB (school) status,this is now broken into 3 stages, a new game will show you grades and stuff, and it will get confusing. take note that pretty much ALL teens are now part of one or another club, convince the teen to quit the club, Add the teen to your family through cheat menu temporarily, It's a little complex, long, probably not even worth it, but it worked once.

I found a workaround but it only worked 1 time out of 10 new save games attempts.

There are around 2 stages for teens now and it all runs on a single script which I find baffling if it wasn't intentional. Game devs heavily modified teen age statuses. There are multiple reasons why this doesn't work properly even with the inappropriate mod.