Do we think a dumb phone Nokia and calls only SIM is just as good (to avoid all the drilling etc. of installing landlines in each kids room?)
Ooma has a wifi box that you plug your handset into. It's not like a POTS where you need to put a jack in every room.
I believe cordless VoIP phones are still a product one can purchase new.
They need only an electrical outlet for the charge stand.
I dug out an old Motofone (the $40 eink candybar) for this reason, only to discover that it’s 2G, which has been decommissioned. Too bad, would’ve been fun to watch the kid learn T9.