Sesame Street has an app that is free. It’s occasionally buggy and will freeze when loading a video, but if you’re with your kid while they play that’s unlikely to be a problem since you can just close and reopen the program.
The app cycles through different games every few weeks, and has a bunch of clips from both recent and classic Sesame Street (biased towards modern but what can you do).
The games are fairly simple, like matching shapes or colors, and generally don’t have fail states. Stuff like throwing the right colored trash at Oscar’s new jacket so it can be properly stained; new trash will keep rolling across the conveyer belt until they get it right.
Idk if it’s actually the best, but my 3 year old is very fond of Sesweet phone, and looks forward to D&D night, the only time we let her have her iPad for more than 30 minutes at a time.