If the kids aren't school age yet, there are definitely a lot of options available, as other people have mentioned.
However, if they are school age, one break that my kids have that qualifies for Kids Sale Free is Fall Break (mid October for us). I'd look into that if the kids in question have a fall break.
Yes, we had to get a room that accommodates 4, but it was still substantially less expensive than having them pay normal 3/4 passenger rates.