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.
Modern dumbphones exist: https://www.hmd.com/en_int/nokia-3210
You can buy a new feature phone with 4G for peanuts.
2G to 3G converter ftw!
Modern dumbphones exist: https://www.hmd.com/en_int/nokia-3210