Check the weather forecast to see the projected temperatures for Anaheim, California during the length of your stay. This will allow you to bring just the type of clothing you'll need.
Leave most of your toiletries at home. Check with your hotel or motel to be sure they provide samples of shampoo, mouthwash and lotion. Purchase travel sizes of the items they don't offer. Most accommodations also feature blow dryers, irons and extra pillows, so leave those bulky items out of your suitcase.
Take advantage of the hotel laundry service. Having your clothes washed on the premises will allow you to wear the same outfit repeatedly, meaning you'll have to pack less overall.
Pack singles of larger, heavier items. Wear one comfortable pair of shoes so they won't fill your suitcase. Bring one dark-colored sweatshirt that you can wear on several cool nights.
Ask your kids to leave most of their toys at home or to fill only light backpacks that they can carry. They'll probably be eager to buy games and souvenirs at the California Adventure gift shops.
Look at each item before you pack it to decide if it's truly something you'll need on your trip. Remember you can buy most clothing, toiletries and living essentials in or around the theme park and hotel if you really need them.