Microsoft child account login issue

Cross-authentication betwen Minecraft and Microsoft account seems to be failing.

For the two child Microsoft/Xbox accounts linked to my parent account, a “welcome back/let’s go” dialog box appears at each stage of login to confirm the Xbox account being used - this happens twice while loading the launcher, and again when hitting “play” from within the launcher to start bedrock edition, or when trying to launch a Realm directly from the launcher. The same “welcome back/let’s go” dialog appears when launching minecraft from the Windows start menu, or from the Xbox app.

The launcher shows the correct Microsoft/Xbox account, and shows the Realms linked to it, so cross-authentication appears to be working at that stage.

When minecraft loads, signing in fails and the default local profile loads, rather than the expected Microsoft/Xbox profile. Pressing “Sign In” leads to an error code “Drowned”. Access to all online content is absent (realms, marketplace, mods, friends etc).

The issue appears spefic to the two child accounts. The “welcome back/let’s go” dialogs do not appear when launching from the parent account, only the child accounts. Minecraft launches without issue using the parent account, sign in succeeds, and realms/marketplace/mods/friends are accessible. If a child account is logged in to the launcher from another machine or windows login, they appear as online in the parent friends list.

Additional tests:

Logging into the minecraft launcher using a child account while logged into Windows from a parent microsoft account does not change the behaviour

Logging out of the child accounts on the launcher, Xbox app and microsoft store, and logging back in does not change the behaviour.

Uninstalling and reinstalling minecraft and the minecraft launcher does not change the behaviour.

Resetting the child account Microsoft password does not change the behaviour.

Running repair tools from the Xbox app does not change the behaviour.