When do you think is appropriate for LOs to start apologizing to other children that they hurt, or to you as a parent if they hurt/disobey? If they refuse to say it, when do you insist, and HOW do you insist?

LO is 21 months and fairly verbal, and has used the words "I'm sorry" before, but I don't think he grasps the concept of apologizing for hurting someone. At the playground the other day, he grabbed and twisted a little girl's shirt, so I tried to ask him to say he was sorry--he didn't, and I didn't insist or make a big deal, but I did apologize to the little girl, and explained to him that we keep our hands to ourselves and use only gentle hands on the playground.

What do you do in those situations? I hate seeing parents badgering kids to just say "i'm sorry" so they feel like the situation has been resolved, especially when it's clear the kids are saying it just to say it, or don't really understand why what they did was in appropriate. Thoughts?