This would be normal and logical for me too but if the account is in the child’s name, some banks require you to prove it’s going to another account in their name and/or why the money is being removed. Total overreach but I experienced it with a cantonal bank.
There was another post on it with more details and the fix was to transfer out of my cantonal bank to another bank (Migros) with a more logical policy so I could take the money out and invest how I wanted (crazy I know)….