Right now my son's iPad has same iCloud account as me. It seems in order to enable parental controls, I need to give him his own iCloud account. Is that really necessary? I can I do it with the same iCloud account?
Everything in iOS is designed to believe that "account" = "person" and any attempt to trick it will only lead to heartbreak.
You don't have to create a full iCloud account for your child, though. There are family-plan-based children's accounts that you still control. His iPad will be on "his" account, yes, but it's still an account you have full control over.