Do you use packing bags...the kind where you compress all the air out before you place it in your luggage? Did you know you can also use the resealable 2.5 gallon ones. Just place your clothes inside, seal the bag part way, sit or squish the air out, and finish sealing the bag. It takes up less room in your luggage.
You can also group clothes together and place in one bag. Or, have your kid's clothes in one resealable bag and yours in another. You could even do one outfit per day per bag.