Hi Michael!
That is a tough question! When you have children with large age difference or with big differences in interests, it can be difficult to strike a happy medium!
One of the first things you may be interested in learning about is the
Rider Switch Option. If there are rides that your older child is interested in, but the young one is just too young, be sure to ask the Cast Member at the ride if you can do the "Rider Switch". Basically, the parents can each ride separately with the older child while the other parent keeps an eye on the youngest. This really is a time saver!
Another option to consider is a mid-afternoon break at the resort. All Disney resorts have wonderful pool complexes and a variety of activities each day. The tween may have fun hanging out poolside or participating in these while the youngest enjoys a nap.
Character meals are great for any age. They are a stress-free way to meet a few characters while you refuel - without long lines! Our family's favorites are the Crystal Palace at the Magic Kingdom and Chef Mickey's at the Contemporary Resort.
Many rides do not have age or height requirements, so you all can enjoy them together. Be sure to look at the Park Maps before you leave home. Pick out the rides that interest you the most and that do not have age or height restrictions. Ride these as soon as your arrive in the morning, and you'll have some happy kids!
Last, but not least, don't be afraid to split up. One-on-one time with each child is a great way for each parent to spend some quality time enjoying each child's favorite activities. It can also make for some fun dinner conversations later in the day too!
Enjoy your trip! I hope its magical!