If the order is being violated, then you’ll have to take it to the court, I believe.
Is the tardiness extreme?? Or is it a few minutes or and hour at most? If it’s not extreme, I would allow some latitude and not make a huge deal about it unless you have already planned something with the kids that required them to be home at a specified time. My ex habitually brought the kids home about 30 minutes past to ‘posted time’ and I just blew it off. No big deal as long they let me know they’re running late. I don’t think he did it intentionally.