Looking for a mod

[Caspin]

I have definitely seen things about curfews in the menus for SP.

Alternatively, if you don't want to do it via SP, you can apparently ask the parent who has issued the grounding to forgive the kid, or you can make the kid do a bunch of chores until they are forgiven. I don't have Generations (I am presuming that this is where the grounding comes from) but I read somewhere about this bug of not being able to go to school and that was the solution put forward.