If you have children, especially elementary school-aged children, they can be very hard to reason with when you're trying to sell your home because it just doesn't make sense to them why they have to pack so many things away or why they have to keep leaving the house for showings. They've never done this before, and it just feels like they're losing control of their "stuff", and their schedule just isn't normal anymore.
The best thing to do is get them involved so they're part of the team, and can have a say in the process. Here's a great article with tips of how to get your kids on board:
One thing that we've recommended is to give them a plastic bin to keep their favourite toys and games, so the others can be packed away and then opened back up after the move. If you get the size that fits right under their bed, it will make the house feel more spacious and not take up precious closet space.
Another thing we recommend is packing dinner during nice weather and going for a walk to the park during showings, or going to Grandma's for dinner, or out to eat.