You could easily give them a basic iPhone with full lockdown on every app with just basic communication and internet browsing abilities.. why not that option?
iOS screen time/parental controls are a joke to bypass. To be clear I'm not aruging that parental controls are bad or not worth it--I'm arguing that Apple's built in mechanisms fail far too easily.
Why spend a few hundred dollars to turn an iPhone into a $50 phone? Feature phones give you communication and basic (if often painful) internet browsing abilities.
https://protectyoungeyes.com/12-ingenious-screen-time-hacks-...