Some relatives of mine with two kids have a 45' Country Coach. It is beautiful and it has two bathrooms, which is a good feature with two kids aboard. Their only issue is that they have to carefully plan and research their stops because so many parks just can't accommodate a coach that large. It's not necessarily the size of the site but the interior roads, tight turns, etc.
Personally, I wouldn't want anything nearly that big. Our 36' DP was plenty roomy for the two of us and had more storage than we really needed, even when we full-timed.