Perfect ages to do Disney! They will love it.
We booked our entire vacation through the Disney webite and had a great time. They took care of everything and we were very happy with the service. We did not need to rent a car because we stayed at a Disney Resort. Disney had a nice shuttle waiting for us and we did not have to pick up our bags at the airport because they had a service that did it for us and delivered them to our room. (At no extra charge!)
For a more economical plan, you may want to try VRBO.com, which stands for vacation rentals by owner. You can get a house with a pool for very reasonable rates. If you don't mind cooking a meal or two, you can really save on the food costs by doing breakfast and dinner at the house.
The only other advice that I have is to get the autograph books the minute you walk into the park!! Splurge and get the ones with a page for the autograph and a slip for the picture. It was a great keepsake for our kids.
Bottom line, there is an overwhelming number of places and choices for you. If anything, check the Disney website just to get ideas of what the hotels look like and if any of them fit into your budget. Then you can take that info and use another service to book or look for cheaper prices.
Good luck and have a fabulous time!