I Have a Big Family

So my youngest brother is going through a you stealing and hitting phase. Mostly from my youngest sister and son who are both smaller than him. Today after he did it At play group and this time bit the kid when he tried to take it back. My mom has had enough when she got him home. She set up the extra pack and play and threw in a few toys and told him til he can play like a big boy he will play in a playpen like a baby. Then to kinda run it in she told me to leave jay out of his which I sometimes but 38th so many lil ones around the playpen is really safer for him. Eli don't like it At all but mom is ignoring him hoping it will stop his behavior