Children do not only have to prepare for the move physically. But more than anything, they need to be emotionally prepared too. Teens would give a strong reaction about it. Smaller kids would be afraid and confused. That is why you need to explain and make them understand the situation. At least, make them feel secure that you will create a home in your next house. The sooner you tell them about the move the better. It would be better if you can take them to see the new place or at least the city before the move. If this is not possible, you can also research about the new place together. Focus on the positive things and on things that will make them like the place. This way, at least they would have something to look forward to.
Since you would be busy packing your things, you can have bigger kids pack their things themselves. The smaller kids can pack their own favorite toys. This would give them something to do on moving day. They would be occupied so they will not get bored and you will be able to avoid tantrums.
You can also allow them to help in unpacking. You can even ask their opinions when decorating the new home as well. This would surely make them feel they are part of the move and the whole family.