Limiting child phone contacts and groups

I have two daughters and am trying to be uber careful about phones. I have a sim card in one but no the other, effectively she uses it as an ipod. My aim is to try and mnitor who they are adding to there contact list. I have found they also keep getting added to large group on imessage that they either dont wamt/i dont want them to be in. And then they darent remove themselves. Both have individual appl id

Question 1. Is there a way to approve the contacts on both phones?

Question 2. Can i restrict the group particpation?

many thanks