We know that buying and selling a house is a very stressfull process. It involves a lot of changes to our life and to our routine. Children more than adults are creatures of habit. It's so important to explain to them the whole process when you're getting ready to move. It might be something that never occured to you that they find scary.
I had a client that told me that when the movers came to take everything out, their son was hiding in a closet. He thought the movers were going to pack him up and put him in the truck. He saw everything that he loved being picked up and hauled off. They had to tell him that everything was going to the new house and that he would see all of his stuff again.