Purchase a set of different colored permanent markers and marker the tag or inside the rim of the item with that color. As you are sorting the laundry, you can quickly tell which child which outfit belongs to.
Also, purchase a laundry bag (like ones used for dry cleaning at home - ones you can wash and dry) and have each child put their underwear and socks in those bags. You can then wash the bags together and sort those items with ease!
