Not the protocol, the group chat UX. iMessage gives kids easy access to a place where they can create groups, name them, invite and kick out other kids at will, and send messages + audio/video. It's minimally different from Snap or Discord - except that those actually have parental controls, and there is no easy way to disable iMessage group chats.

The equivalent is simply lacking from Android due to RCS group chat being a broken mess.

> create groups, name them, invite and kick out other kids at will, and send messages + audio/video.

All of that has been (and still is) available on everyone's phones since the dawn of time except for "name them": https://en.wikipedia.org/wiki/Multimedia_Messaging_Service

  - create group: send an MMS message to whoever you want in the "group". Now you have a group chat.
  - invite people: send a new MMS message including all past participants and the one additional participant.
  - kick them out: Send a new MMS message including all past participants except for the person you want to remove.
  - send messages + audio/video: MMS supports all of this.

I'm surprised you seem to presume that WhatsApp, Discord etc. wouldn't immediately fill the gap.

At least in Berlin (School and Uni) my experience was that WhatsApp was far more prevalent already (due to more mixed Android/iOS environment likely).