My 3 yo borrows my iPhone when we ride home from kindergarden and I don't want that he fells asleep. So he watches an episode of Fireman Sam on Amazon Prime or plays a game. He unlocks the phone with his "magic finger" and after 20 min I get my phone back.

It would be so fantastic if he could just start HIS apps and would access a restricted Prime account. My 6 yo is the same and since he was 2 1/2 I switched by iPhone twice. So I don't see the case that it's not important as they will get their own ones when they are 8 or so - that's 5 generations of iPhones.