I have not investigated this, but you should not need to stop/delete child actions as well. I’m not sure if what you are seeing is expected behavior or not, but it doesn’t sound right. ( perhaps the child actions stay open, but don’t actually do anything ? )
This also appears to be true for multiple action groups. My code is creating a mag and uploading it. After it goes complete, when I delete the mag, all the member actions still appear to exist in an open state.
If I delete the mag, the status for the mag shows something like this,
/api/action/4006/status
4006Stopped40074008
If I look at the status of a particular member action it shows open,