Walt Disney World has a great policy (that is not too well known) for families with children that are too small to ride an attraction at Disney World. It is called a “rider swap”. This allows the family to wait once and take turns riding the ride without having to get back in the line and wait a second time. Every ride has a different way of doing this so be sure to ask the ride attendant at the attraction entrance what the procedure is for the “rider swap”.
Here is an example. In Epcot we wanted to go on Soarin’ and there is a height restriction of 40 inches. I had children under that. One of us stayed off with the baby while the others waited in line and went on the ride. We were told to wait in an area by the entrance. When they got off the ride they came back and one of the previous riders waited with the baby and we went on the ride. They sent us through the fastpass line. If you have children who are over the height restriction they can ride twice (once with each parent).
Like I said, each ride has a different procedure since the layout of every ride is different. Be sure to ask the attendant at the entrance for a “rider swap”.
Also, be sure to check out the height restrictions for rides before you go. You don’t want to get your kids all excited to ride Big Thunder Mountain Railroad and then find out one of them is too small to ride it. They will be so disapointed. We always know ahead of time our children’s heights and what rides they can or cannot go on. Then we will separate and do something special with the younger kids while an older one rides a big ride. That way the younger ones don’t feel like they are missing out. You can find out all the restrictions on height here.