From what I understand if it is for a minor then and adult would be the "main" person to set up the DAS for the rides. How it works is, you go up to the ride you want to go on and tell the cast member at the entrance you want to set up DAS. They take their handheld and scan your ban and I believe they ask you for how many people. Then they give you the return time. They do not make the child scan because people were concerned that the autistic children might have a problem seeing the ride and not going on it right away so they made it so an adult can set it up. You will need to talk to Disney about this when you get there. I am sure there is a way for them to have it attached to both of your children. I doubt your family is the only one with this issue. I would not worry about it, it will work out. What is nice about it, the return time shows up on your My Disney Experience so you do not need to remember the return time.