I have had one messy move with one almost-two-year-old. I'll be moving twice more this year, so I'll share any wisdom I gather. But for now, learn from my mistakes and lucky guesses with these five tips:
1. Pack the children's rooms last. They'll feel more secure if their belongings are in order, and it may help them sleep better leading up to moving day.
2. Let them help you pack their own things. If they are putting their toys and other things into boxes, and watching you, they'll feel less worried that all of their things are being taken away. Even if young children are unpacking as much as you're packing, they'll feel included. Reassure them that they are being put into boxes so that they can be taken to the new home, and that they can be played with on [x date].
3. Try to have fun. Everyone would likely agree that the process of moving brings frustrations. Children are known for finding the joy in simple things. Join them. Let them draw pictures or scribble on boxes*, and save on big empty box as a fort.
4. Keep a suitcase of must-haves with you on the move. This may be a bag for each child, with their special security item (blanket, stuffed animal), their bed linens/pillow/blanket, and night routine supplies (toothbrush, pacifier, pajamas, diaper, night light), plus a snack and a change of clothes.
* Dry-erase markers wipe right off of skin (more easily than washable markers) and usually wash out of clothes. Hilighters stain everything, like the couch, the recliner, clothes, unpacked dishes....