Like most theme parks many rides have some kind of height requirement. If you are traveling with little ones who are not tall enough to ride you you can participate in the rider swap. Basically 1 adult and other children who are tall enough would ride while the 2nd adult waits in a designated area with the child who has not met the height requirement.
Disney World also offers a something similar to families but we really like how Universal does it and here is why. At Disney all members of the party have to walk up to entrance and scan magic bands and then the first half of the party waits in line and then 2nd half gets a fast pass once they have returned and can switch off. Universal is so much better because the whole party gets to stand in the line together and once you get close enough to board the ride the 1st half continues on while your little one(s) and other grownup get to hang out in a nice air conditioned room.
The rooms are themed to fit the ride and have a TV playing videos also themed with the ride. At the Harry Potter ones the Sorcerers Stone was playing, in Jimmy Fallon family friendly clips were being show. A few of the rooms even offered a diaper changing station which was really surprising since the bathrooms in the parks did not always have them.
Now you do not have to use the rider swap if you would rather take your little ones to a play area instead that is a great idea too. But if all the adults in your group want to ride but have children that do not meet the height requirement for the ride then I would highly recommend taking advantage of this free option!