It depends on what the criteria is for a "best" option. If price is the criteria, I would suggest one of 2 options -
1. Fort Wilderness Cabin. These will sleep 6 (for in bedroom, and 2 in living room).
2. 2 All Star (or Pop Century) connecting (not adjoining) rooms. Although they cannot guarantee this for regular requests, I have heard that it can be guaranteed when young children are involved.
If a little bit more money is available, then they might want to rent points and get a 2 bedroom at a Disney Vacation Club resort.
If money is not an problem at all, then I would suggest a 2 bedroom at the Villas at Wilderness Lodge (due to the ages of the children). Or, at the Beach Club (where they can swim a Storm Along Bay).