Some of the CMs require you to "show" your kid! Space Mountain is kind of a pain...you have to walk up to the line show the baby, then they give the other adult a card on a lanyard, then they give you the ride swap after you get all the way through.
On star tours, they like you to wait with your family until the door, but they are not too picky, just go up to any CM and ask! They are very friendly