As the primary visitor center for the Philadlephia area, this center is a must see! Almost brand new, it has many fun and exciting and user-friendly attractions.
Its location is probably the best attraction of all- right in the middle of Independence Hall, Liberty Bell, and other historic sites.
Across the river from Philadelphia, and a bit closer to Mount Laurel, this up-and-coming area has all kinds of family-friendly locations. There's the New Jersey State Auqarium plus lots more!