Nope. See a cast member at the ride prior to anyone getting in line. Be sure that you have the too-short child with you. The CM will give you a rider swap pass. The first adult can then go through the line with whichever kids want to ride and you can wait outside with the child who can't ride. Then, once the first part of your party comes off the ride, you use the rider swap pass to go through the fast pass line. The rider swap pass is good for 2-3 people (depending on who you talk to...), so older children can come with you and re-ride if they want to. My daughter has loved getting extra rides on things her brother has been too short for.
ETA: You also don't have to use the pass right away. You can pocket it and come back at a later time, or even another day. The passes they were handing out in mid-March were good through the end of the month.