I would love to see the success rate of getting the parents of the child’s friend to set up a matrix client for their child’s one friend that doesn’t use anything they do.

Help your child embrace not needing to be constantly in communication with her friends, to (gasp) use the phone …. or accept and monitor the evil empires’ offerings but no matter what you do, don’t for one second think you’ll get a single family to set up a matrix client for “that one kid”.