Unfortunately no solution in MCPE-120083. Neither the patch from MCPE-230429 has worked as it seems.
In my opinion this problem still exists on the Nintendo Switch Version 1.21.124 of Minecraft:
Login with parents' account works fine.
Login with child account fails repeatedly with error code “Drowned”.
Unfortunately, this problem is still unresolved for Nintendo Switch. See the ticket MCPE-232324 (which has been marked as duplicate of this).