Brought our 12, 11, 9, and 5 year old on this bike tour. Some of the hills were a bit hard to do when going uphill dragging a 60 lb kid on a bike attached to mine but going down was better then any roller coaster. Plenty of water fountain and benches along the trail made it very manageable and fun. You should be in relatively good shape though to do this. Old Town Alexandria is beautiful to just walk around in. Good deal for your money considering entrance to George Washingtons plantation is 20 a head. Overall we had an incredible experience.
Encountered friendly fellow bicyclists on a hilly, but doable trail. Water stops along the way. Leafy trail. The history at Mount Vernon was palpable. Bike pick up and drop from was easy. The Potomac River Cruise was a perfect end to a hot, yet enjoyable day.
Nice bike ride, but beware of doing the 10 miles in summer. Very humid. Would recommend though.