North Shore Lake Tahoe and Truckee in California. Sunny during the day and cool nights. Plenty of activities such as swimming, boating, biking, hiking and rafting in the Truckee River.
A good vacation destination for parents and kids are the Ainsworth hotsprings located outside of Nelson, BC. The hotsprings run through a cave, making them very interesting to young explorers.
Walt Disney world is a great place for families vacationing with small children. The parks are open from 9am to 10pm most nights and after a long day they offer value resorts for you and your loved ones to relax in as well a pools to kick back and cool down in.