1. Include them in the job
Even though they're little they can complete small tasks (even if the tasks aren't relevant sometimes it's just good to keep them busy) for example, we asked my littlest guy (1.5 yrs old) to take all the crumpled up paper into the garbage or another box - which was just fine with me!
2. Prepare them well in advance
We bought a book about moving for our 3 yr old and talked about all the great things about our new home. It helped him understand the concept but for some reason he got it in his head that he was getting a bunk-bed at the new house and he was devastated when it was his regular bed (be careful not to accidentally over promise).
My biggest worry about moving was the door being constantly open and heavy things being lifted around little curious kiddos. So this is probably the most important tip, get a babysitter for the move-in and move-out. Even if it's just someone to watch the kids in the backyard and keep them out of everyone's way.
With the babysitter or grand-parents still around, get the kids beds set up first. At least for me and our kids, sleep is something we have strived to keep consistent from a very young age. Getting their beds set up first provided them with comfort and a sense of home right off the bat.
As parents we know, kids like to play with boxes often more than the gift so moving is like Christmas. We let the kids have fun with the boxes - making storefronts, rockets, forts, colouring on them etc. The kids loved this.