The 1.2.10 update appears to have resolved the issue of the game crashing immediately upon log in with a child account on Windows 10 as well.
I am in the same position as CodeMonkey with my two Child accounts but on Windows 10 and Android. Signing out and signing back in doesn’t work for me. The game still crashes almost instantly.
I did what Spike Beer suggested for my two child accounts. I saved their privacy settings again from within my adult account but did not have any luck.
The two accounts I am having this problem with are also Child accounts. My Adult account works fine.
I didn't have any texture packs applied either.
I have been experiencing this same issue on WIndows 10 and Android. If I log into either device with my XBox account there are no issues but when I sign in with either of my kids accounts on the same device Minecraft crashes.
Festive Pizza Delivery Sim by 57 Digital
Upon purchasing the above mention game and selecting the download option the menu is stuck on the update option and the create world never shows up.
I'm having the problem on the Xbox Series X and my Samsung Galaxy S20