Say you have two parents and one very small child (such as a baby) but you both want to ride. Instead of him queuing while you hold bub, then her queuing while you hold bub (which could take hours some days on some rides) you queue together, tell attendant at front of queue you are doing a "child swap". One gets on, and the other waits at front of queue. When ride ends parents one gets off, takes bub, parent 2 gets on and takes ride.
OR say you have 2 kids - 1 old enough to ride (but not alone) and one not. Same as above, except that parent 1 rides with elder kid, while parent 2 waits with younger kid. Then, at end of ride, elder kid stays on and parent 2 joins them. So, child gets 2 rides and mum and dad both get a ride with their child.
Of course, if there's no queue, or only a little one, it's probably easier for you to just take turns! (Except on a ride like Indiana Jones where the entrance to the ride is actualy hundreds of metres from the actual ride - the rest is a very loooong underground queuing system).
