Hi there Trish,
You can certainly change rooms as long as there is availability at the resort of your choice. To check availability and pricing at a different resort, you can call (407)WDISNEY.
Based on the situation you've described, I think you'd really love
Port Orleans Riverside! Like Caribbean Beach, Port Orleans is classified as a moderate resort and should be comparably priced.
The rooms at Port Orleans Riverside have just undergone a renovation and the decor is beautiful and just like brand new. The rooms now feature two Queen beds which sounds like a perfect match for your family! It is my family's favorite moderate resort and it really has an intimate, boutique-hotel vibe that we really enjoy!
If you have your heart set on Caribbean Beach Resort, you may be pleased to hear that there is, in fact, an option to book a room with a King bed. Rollaway beds are available for a fee on a first-come, first-served basis and cannot be guaranteed.
Best Wishes,
Amanda F.