some great campgrounds in WA for kids:
1) Kalaloch (Olympics, need to make reservations months in advance)
2) Heart of the Hills (Olympics)
Easy day hikes:
age 4-5: Rattlesnake Ledge, Heather Lake, Hurricane Hill
age 6-7: Lake 22, Pilchuck, Snow Lake, Spray Park
age 8-9: Heather Pass/Lake Ann loop, Melakwa Lake