@children targeter does not work for players.
When trying to use @children to target entities spawned by the player, <caster.children.size> returns zero and @children targets nothing. I've tested with a mob which messages it's @parent and it is actually setting the mob's parent to the summoner, just that @children isn't working at all.
This makes summonable minions an absolute nightmare without GOOP. Not sure how long this bug has been present, using the latest MM dev build on 1.20.1.
Reproduce with this skill. https://pastebin.com/pM7FNxkB