Connecting rooms is a request, not a guarantee (despite any wording that might appear on your reservation confirmation).
Check in EARLY, and indicate your willingness to wait for connecting rooms to become available, however, even then it's not guaranteed.
Travel with only one adult, and four children between three and seventeen. Still not guaranteed but more likely (since one or more of those children would otherwise have to be in a room without an adult).
Book a room at Port Orleans Riverside - the Alligator Bayou section sleeps five, but one should be relatively small, to fit in comfortably in the trundle bed.
Book a room at a Deluxe resort that holds five people.
Book a Family Suite at the All Star Music resort.