For Great Wall, my hotel provided a driver for around USD$130 who took me to Mùtiányù, gave me 4 hours free time. They have a cable car to get up to the wall, and you can take a bobsled down which was very fun! I went last Feb and had the place to myself - if you can swing a private driver, definitely head to Mùtiányù.
Summer Palace would also be nice with the family, take metro line 4 to Beigongmen.