Hi,
I have a 2 yo and a 4 yo and in the last year we did a 9 day trip to WDW and a 2 day to
Disneyland. It sounds like our 4 yo are the same, and my 2 yo in line does a combination of standing, being carried, rolling on the ground. It is tricky but a couple tips.
First, we did rope drop every day we went to the parks because that allowed us to crank out the most amount of rides with the shortest aggregate wait. I know this sounds obvious but I did a lot of planning strategy not only on FP but also geographically on how close things are in the park so we could maximize what we were doing in an area.
Second tip is if you know it is going to be a longer line, save the snacks for line if possible. If we picked up a go go squeeze or lolipops or whatever, we usually waited until we were in the line. Obviously you don't want an ice cream cone melting everywhere while your kids are bumping into other people, but just best judgment. Also, drinks are probably a no no as you don't want a bathroom emergency in a longer line. In terms of rubbish there is almost always a barrel at the front of a queue, and separately we always had a spare mesh bag for trash.
Third, the queues now are not like how they were when I was a kid 30 years ago. There is a lot to see and do in the line, so you just need to point it out and get them engaged if you can.
Fourth, and this is obvious but hard to execute, just relax. Your kids are going to have their moments. If you break they will break. I remember my dad always saying "WDW is the child abuse capital of the world" - there are people all over the park having meltdowns - kid on parent, parent on kid, kid on kid. You won't be alone, just keep your cool. If you do I can promise you the good moments will far outweigh the meltdowns. A year out from our first trip with the kids, I don't remember a single fit they had in the park even though I know they had them, really all that sticks with us is the things we all enjoyed.