I've added multiple children with the same name to parents before. Never had a problem.
Does it hard stop you from adding them, or is there a warning box that says the information is suspicious?
If it's a warning box, you can click whatever the button is that says "Okay, I understand that you think something's wrong, but I'm going ahead anyway."
I think WikiTree would only hard-stop you if you didn't provide any dates (birth or death).