If your kids are of school age, they are old enough to be involved in the process of moving. Keep in mind that it’s very displacing for kids to move. If they have no involvement or “say”, they often feel very against the whole idea. If, on the other hand, you include them, they are much more likely to have “buy in”. I am not suggesting you let your kids choose your new home, but, depending on your specific family, you can decide how much influence they should have.
From a selling perspective, take the time to explain to them (use online pictures of other homes for sale) how much better your house will look if it’s kept tidy and how it will sell quicker if it’s neat. While they may not be in a hurry for it to sell (if they don’t want to leave), you can mention that the faster it sells, the sooner they will not have to keep it so neat and leave every time someone wants to show it. If they are invested in the end result, you may see more participation. Of course, if they are excited about moving, you should be sure they know that houses that show well tend to sell faster.
Another thing you can do is encourage your child (or do it for them if they are too young) to photograph the spaces he loves, like his bedroom. That way, if he wants to recreate it in the new place, he will be confident that he’ll be able to. Remember, while some kids are excited about a new house, change is very hard for others. Similarly, make sure you child has the opportunity to say goodbye to local people and places if you’re moving away from the area. A goodbye party which includes exchange of contact information with important people is a great way to inject some excitement into the process.