Hi Tracy!
First of all, congratulations on your 1st Disney trip! You're only days away! Be prepared for tons of fun, memorable moments, and being a kid all over again (smile)...
OK. First trip with 2 girls and a boy? I'd have to go with Chef Mickey's located at the Contemporary Resort. Chef Mickey's features Disney favorites Mickey, Minnie, Goofy, Donald, and Pluto. It's not the only restaurant with the "Disney Fab Five," but probably the most popular. A number of guests enjoy the fun ambiance and experience of Chef Mickey's, and like the location at the Contemporary, which is located literally right across the street from Magic Kingdom. You can drive to the resort if you didn't have any other plans, or, if you're planning to stop at the Magic Kingdom, you can take a little break and catch the monorail right on over to the Contemporary Resort.
Eating here is a great chance to get those special pictures with Mickey and Friends without having to wait in the Meet and Greet lines for long periods at a time. It also serves a good balance for your son, compared to the number of princess dinings on Disney grounds.
The food is also good (American style with chicken, beef, mashed potatoes, etc). and also a good Children's menu for dinner!
The only thing is try to call to see if you can book a day and time. Being this close to your arrival, and peak season, many of the restaurants may be booked. But who knows? A lot of guests change plans, so there are cancellations.
Good luck on your 1st trip!