Washington DC has so many great museums. It can be overwhelming, and even a little tiring with so much to see and do.
I’ve learned that when I have kids in tow (of all ages—my oldest is now 23), don’t try to do the whole museum. Have a plan for each museum–that you’ve hopefully figured out ahead of time (I can help you), or that you figure out at the Information Desk when you walk in. We usually spend between one to two hours tops in a museum. I want my kids to like going to museums, not dreading them, and walk away with something they remember.
I always try to end a museum visit with something fun. Usually for us, it is just a picnic on the Mall, (the grassy area between the Capitol and Lincoln Memorial, and in front of most of the Smithsonians) with a ball or Frisbee. Or it could be a carousel ride or a snack.