We are a family of 5 as well and we went on our first family trip to WDW last year when our kids were exactly 5, 4, and 16 months. We had a blast....so much fun that we immediately began planning for our trip that we just completed in April. I don't know how tall your 4 and 5 yr old are, but that will determine your ride choices. Become familiar with the rider switch, fastpass, etc. Most rides we could ride 1 adult, 1 child; and 1 adult, 1 child, 1 toddler - like Dumbo, Magic Carpets, Tricertop Spin, Winnie the Pooh, etc. Our boys were over 40", so we were able to take advantage of the rider swap. We would get Fastpasses for Big Thunder Mountain and then we would all go to the Fastpass entrance and tell the CM that we needed to do a rider swap. They would give us a rider swap pass and then 1 adult and the 2 kids would go ride the ride (we could all fit in one row) while 1 adult and the toddler waited at the exit. When they got off the ride, the other adult and the 2 kids would go back through the Fastpass entrance and ride the ride again. It worked out well...the kids get to ride twice with a reduced wait time. We never had any problems with our family of 5 fitting on a ride. In a few years, I doubt we will be able to fit on them like we do now just because our kids have grown, but by then, they will be old enough to sit in there own seat. To get more advice, I would head over to the Theme Park stragies board. They have some great advice. Also, if you go to the Mickey Mom's panel they do have some great advice concerning families of 5 at the parks. Good luck.
