I think the key to successfully traveling with kids is to severely limit the scope of your objectives.
My philosophy during this trip is to find one activity per day and spend approximately 4 hours round-trip involved in it.
No matter your age or how you are traveling, it is impossible to 'do it all.'
By setting unrealistically high standards for a family, you are preparing yourself for stress and disappointment.
It's just not worth it.
Pick one thing. Do it well. Declare victory. Go home (back to where you are staying, I mean).