An idea - get fast passes and do child swap when possible.
We have two kids, an 8 month old and a tall (42") 3.5 year old. One person stands in the regular line - or fastpass if we have them - with DS if he wants to ride. After they ride, then we can go on, without waiting in line. There's a designated place to wait. I've been given child swap passes before and also just told to wait in a spot - so I guess it depends on where the child swap is. Then person who didn't ride then gets to ride - and DS can even do the ride again with the other parent! When I was given the passes, they always gave me two so DS could ride again. I think they can give up to three.
*If DS doesn't want to ride, you can still get passes. The idea is that the parents (or other people travelling) will both be able to do the attraction no matter if the child wants to do it or not. We have found that if DS doesn't want to do a ride and knows this at the start that we're better off just using fastpass and having DS in a play area instead. He's not going to wait in line for a ride he's not going on. And some rides have small waiting areas which are hard to contain him in if he's just waiting for us.