Do you have a reference. The only thing I can find that seems to apply to a bnet account (not a particular game account) references “children” and does not state a limit:
Subject to the laws of your country of residence, minor children may utilize an Account established or play a Game installed by their parent or legal guardian upon the parent/guardian’s acceptance of this Agreement. In the event that you permit your minor child or legal ward (collectively, your “Child”) to use an Account or the Platform (including any Game), you hereby agree to this Agreement on behalf of yourself and your Child, and you understand and agree that you will be responsible for all uses of the Account or the Platform by your Child whether or not any particular use was authorized by you.