I agree with the others....keep it fun for the kids.
We've moved twice in the past 2 years and my kids are (just turned) 4 and 19 months. I feel your pain.
My oldest was excited about the new house, but didn't like too many changes in HER room. Keep the room set-up decor as much the same as you possibly can. If new bedding and wall stickers (say, Dora or Diego) would help make it more interesting, do it! That helped us move to this house.
We also just kept explaining that this was our new home, but all of our things were coming with us. Don't forget to explain the family pet is coming, too. They have a hard time imagining what it will all look like and what it is going and what is staying. My daughter kept asking if the stove was going, the clock, the bathtub, etc. She was also older, so you may not get so many questions.
If you have access the new house before your move in date, see if you can start child proofing things like under the cabinets in the kitchen and bathrooms where cleaners go, and a gate at the top of the stairs and bottom. Invest in a really heavy duty gate for the top.
Pack away about half the toys your oldest plays with and keep it marked REALLY well. You'll want to pull those toys out first at the new house. They will be fresh toys to play with making them more interesting when you get there.
Set up bedrooms and the playroom first. You will need a place for them to nap and play immediately.
Try to label your kitchen cabinets with masking tape ahead of the move-in. That way if you have someone helping you put things away, they can work on your kitchen right away - and it isn't personal belongings.
Try to have a staging area that you put things in while you wait to put them away - like the garage or an extra room that you won't be using in a few days.
Take any help you can get!!!! Good luck. It will be the best move for your family in the long run. Remember that. You won't have that stress of a house you are drowning in over your head and feel relieved that when something goes out in the new place YOU aren't financially responsible for it. It really is a relief. :) Been there, done that.