You can use rider swap with any attraction with a height requirement. Your baby will need to be present at the entrance of the attraction, but he / she does not have to wait in line with you.
If you ride in the standby line, you will be given a paper rider swap ticket good for 3 people to ride that attraction using the fastpass line at a later time. The paper ticket can be used at any time, by anyone before it expires (typically on the last day of the month).
If you have booked fastpasses for an attraction with a height requirement, it works exactly the same (you just ALL get to skip the standby line). One sensitivity here is that the person waiting behind with the baby does not need a fastpass for this attraction -- in fact, they can make their fastpass for something else during that window of time that the baby can ride.
For example, my family of 5 (2 adults, 3 kids) wants to ride Mine Train. My youngest child is too short. I would make Mine Train fastpass reservations for my husband and 2 older kids. I would make myself and the baby fastpass reservations for Winnie the Pooh at the same time. All 5 of us would go to the Mine Train fastpass entrance and ask for a rider swap ticket. My husband / older kids would get the paper ticket (or a lanyard to get a paper ticket later in the line), they would scan their fastpasses and ride Mine Train while I took the baby over to ride Winnie the Pooh via the fastpass line. I could then, at any point later in our trip (but before the end of the month), ride Mine Train with my older 2 kids using the fastpass line with the paper rider swap ticket.
You can really make Rider Swap work for you if you remember that whoever waits with the baby does NOT have to ride immediately after the rest of the group (they can go do something else and come back later) and they do not have to have the same fastpasses as the rest of the group.