With the recent Bedrock update 1.21.120 (it’s now fixed in 1.21.121) there was a bug where Child accounts couldn’t log in https://piunikaweb.com/2025/11/03/minecraft-1-21-120-update-drowned-error/
Unfortunately for me I uninstalled and reinstalled to no effect, but had a backup of worlds. Now that the bug is fixed I put them back in the usual “AppData\LocalState\Packages\Microsoft.MinecraftUWP_8wekyb3d8bbwe\LocalState\games\com.mojang” folder….. and nothing happened.
Turns out, coincidentally, the file location has moved out of LocalState into Roaming, which I happened across https://learn.microsoft.com/en-us/answers/questions/5607869/the-minecraftworlds-folder-in-com-mojang-is-missin
The new location is “AppData\Roaming\Minecraft Bedrock\Users\[A number correlated to your user]\games\com.mojang\minecraftWorlds”
Hope that helps someone else!