Having a child with Robert that he (and the audience) knew nothing about makes as much sense as Holly having a son (Ethan) with Luke.
I'm ok with this as long as they do something interesting with it. If there is just the big revelation and it doesn't tie into or add to any of the upcoming storylines then it will be a bust.
Execution is everything. Doing something for the shock value with no plan beyond that will bomb. I'll wait to see how they tell the story before I decide how I feel about it.
Karen L.