Hello, I have been monitoring this thread for over a year, and it is unfortunate that there is still no resolution from Microsoft.
But, there is a work around.
Just purchase a number; set up teams account for your children, and then cancel the number.
I purchased my numbers through numberbarn.com. They were $5.00/each.
If you want, you can park the numbers for $2.00/mo, and then port them over to your child’s cell phone, if/when that time comes, or just cancel the account. Either way, it is easy to then register teams with the newly purchased number, under your child’s family account, setting it up under their email address/profile.
That's a viable workaround 👍
However, people should be aware that by accident or through malice, anyone who subsequently picks up that number (assuming it is let go and not parked) would be able to use it as a username for the Windows account and as a means to reset the password, and even multi-factor authentication.
The question I therefore have, for anyone who has tried this, is whether you can continue to access Teams if you remove the number from your account after using it to set Teams up?
P:ostscript - I've noticed that our kids can access Teams in the Windows app, accept an invitation to join and use the service. It is only while signing in using the Teams app on Android (have not tried iOS) that requires a phone number, however the app requires a phone number even after they have accessed Teams on the web, and it is on Android that they need to access Teams.