Yeah, I'm AP (real AP? lol not wacko just instinct and evidence based practice) and I'd definitely get involved depending on the kids' ages. some kids are just SO like that--you want it so now I NEED it. Getting down and calmly but firmly explaining, distracting, asking them to go blow off steam on their own, all good. Even setting a timer for turn taking. Most of the time a quick start if this leads to my kids working it out very easily. DD5 is a super sharer and DS1 is more jealous but the regular modeling IS helping. I definitely see very permissive parenting at times, sometimes by parents who just let it happen, who just aren't "with it," and yes some who are all "oh he's so spirited" wooza wooza about it all. I think there's something to not being overly controlling but kids should be guided!