Hi Erin,
Your trip is right around the corner, and with all of the planning and research involved in a Walt Disney World vacation I certainly understand second-guessing your choices.
I've made it no secret that Coronado Springs Resort is my favorite moderate, the rooms are larger and I prefer the decor over Caribbean Beach Resort. That being said, what I love about Caribbean Beach Resort is their pool and splash area for little ones. Your children are the perfect age to experience this, and since you are visiting in a month that is typically very hot I would imagine that you could be spending a lot of time pool side.
So if the pool is one of your major factors in determining which resort you stay at, Caribbean Beach Resort is a great choice.
To get a better feel for both of the resorts, I suggest you visit
www.allearsnet.com to look at a huge library of photos of each of these resorts.
All in all, switching resorts would be dependent on availability and I'm not sure if you will have the opportunity this close to your arrival. So just know that if you keep your Coronado Resort Reservation, I don't think you will be disappointed. It is a beautiful resort with a wonderful playground and pool area.
Hope this helps, have a great trip!