Hi, Brenda!
First of all, congratulations on making your first trip to Walt Disney World! You and your kids are going to LOVE it!
Here's an overview of what I recommend, but PLEASE feel free to follow up with more specific questions and details when you can. Where you are staying is really important in making the most of your time in WDW; there are options for almost any combination of circumstances, so I want to be sure that you get the most time and value out of your stay, and direct you toward what's not too far out of your way, as well.
If you don't have the Park Hopper Option on your tickets, then stick with Magic Kingdom Park for at least the first day. For your second day, any of the other three parks are wonderful, but base your decision on the interests of both kids. My kids are also three years apart, so I know that finding something specifically for each one each day is the key to keeping everyone happy. Send me another message: boys? girls? princesses? pirates? parades? fireworks? We can find the perfect second-day plan for you with a little more information. Can't wait to help!
Regarding dinner reservations, you might want to stick with the character dining options both in the parks and the nearby resorts as well. This will not only provide you with a fantastic meal, but also with truly heartwarming photo opportunities that you won't have otherwise, even if you DO wait in line to meet a character in a park. There's just something so special about having the characters come to you!
Here's a link to your Character Dining Options, many of which are not located in a park, so no tickets are necessary.
Again, please come back with more information and more questions. I'd love to help you choose what's just right for your family as you travel to Walt Disney World for the first time ever!