I haven't had a visit from the social worker for years but I think, with EA Story Progression, they can get taken if they get an F in school (could be for an extended period of more than one day). Also they need to have their mood meter low, probably red. You get warnings first. It happens with pets too and then your sim can't get any new pets for ages. I don't know how long. I really don't have much recent experience with this so probably can't be much help.
I've tried that buyable IF dolls mod and couldn't get it to do anything - but I might have just not persisted for long enough.