First of all thank you very much for you replies. I do appreciate you taking the time to comment.
I know they have little more work with two extra people in one cabin, but I don't seeing it being enough that it should require double the tip. You only have to clean the bathroom once, or pick up the room once, clean the floor once, whether or not I have 1 person or 6 people in the same room. If I move the kids to another an adjoining room now the stewards would have to clean up two rooms. Thats two bathrooms, two floors, well you get my point. Now that they really have twice the work they still are not getting any more tip? You can't really tell me that cleaning two rooms each with two occupants is same amount of work as cleaning one room with 4 occupants. Which would you rather do? This is why I am thinking tipping same amout for children occupying the same room is a bit excessive.
This is why I am leaning towards what kryos wrote.