This is on the behalf of a friend so it might be a little light on some details.
A little context: mum and dad were together for their 1st child (daughter now 8) but split up just before son (now 5). Mum and dad are mostly amicable now after a difficult split however dad can be a bit childish and manipulative with the kids when they're with him.
Both kids have gone to dad's fortnightly- monthly (for the most part) since the split. When son was 18 months, mum started noticing bruises on his ear lobes. She took him to the doctors to try and get to the bottom of it but some how found out that dad had been sucking on his ear lobes. She told him never to do it again and he appeared to have stopped. Fast forward to today, son and daughter have come back from dad's and son has bruises on his lobes again. Son says that he likes it, daddy likes doing it and sister does it to him as well. Sister knows not to do it but does it when daddy encourages it.
It seems to be done playfully but it all seems a bit wrong... Any thoughts?