Interesting places to visit in DC

[libramunoz]

Hey fellow GCers,

I have a question for you. My Mom is going to be visiting my brother and his children this month. He lives about 10 minutes from DC. Do you know of any kid friendly (and possibly free) places that she can take the kids to go a visit. The children are ages 10, 7, 3, and 9 mo. old.

Any places that you list would be a great help to me.

Thanks for all of your help!