I have written about it before, but it obviously can't be repeated too often because it keeps coming up: it just is not a good idea to make one of your children a co-owner of your bank account, for at least three reasons: (1) a co-owner can remove the contents of the account without your approval; (2) a co-owner's creditors can collect the co-owner's debts from your account; and (3) after you have passed away, the co-owner doesn't have to share the account with your other children, even if the co-owner promised to do so.
I have seen that third scenario more times than I can count. Needless to say, it destroys family harmony. Isn't the cost of a will worth avoiding that outcome?
The contents of this blog, this web site, and any writings by me that are linked here, are all my personal commentary. None of it is intended to be legal advice for your situation.