Hi Steph, and welcome!
This is from allearsnet.com. You can also do a search on these boards to find more info:
Try the baby-swap. The baby swap is designed to allow both parents to experience an attraction that your little one may be two small to ride and not have to wait in line twice to do so.
It works like this. At the entrance to the attraction, you mention to the cast member that you would like to do a baby swap. They will instruct you on how to proceed on that particular attraction. You will all go into the attraction line and one parent will ride the attraction while the other stays with the child. When the first adult is finished, they will take the child and the second adult will then ride. This is especially fun for an older brother or sister who is large enough to ride the attraction. Many times the cast members will allow the child to ride with both adults which gives the child the chance to experience the attraction twice without having to wait in line.
This procedure is changing for many of the rides that are now offering FastPass so be sure to ask the CM at the entrance of the attraction which procedure you are to follow.