I think we are very lucky here in the UK, the BBC have a channel called “CBeebies” aimed at 0-6yo whith all the videos available through a dedicated app, plus a huge range of games. Absolutely no ads and most have an educational message.

https://www.bbc.co.uk/cbeebies/grownups/article-cbeebies-app...

My 4yo is allowed to use an iPad but it only has the BBC apps on it. No YouTube, Sky, or any other ad supported apps. The BBC has made it possible for us to give her something and not need us to moderate what she is downloading or playing (although we do limit time on it strongly).