How exciting it must be planning their first trip! And they get a whole week of fun!
Disney has an abundance of fun and activities for the entire family. To highlight some of them...
Magic Kingdom
I always say everyone should visit the Magic Kingdom on their first trip. When I think of Walt Disney World, I think of Magic Kingdom and Cinderella's Castle first. Be sure to visit there and take lots of pictures. There are also usually Disney photographers that will take your picture at Main Street with the castle as the backdrop.
The parades and fireworks are awesome! When you visit, check the times for these. Your family should really appreciate seeing them. At Magic Kingdom, the Move It! Shake It! Celebrate It! Street Party is really fun. Also, witness the Wishes Fireworks Show in the evening. Watching fireworks shooting off right above Cinderella's castle, with perfectly timed music, is magical indeed.
Dining
Since you'll be there 7 days, I'd definitely get one of the Dining Plans. Disney has three options: Quick Service, Standard Dining, and Deluxe.
Other Tips
If you don't feel like carrying your stroller everywhere, Disney has daily stroller rentals for your young one that is honored by all the parks.
If you plan to stay at the Disney Resort, and staying a week, I'd take one day just to enjoy the resort and not travel to a park. The resort also will have activities the entire family can enjoy.
Good luck and best wishes for a magical experience!