Everyone who lives near the DC area should take their kid here at least once. Especially when they are young, if they like dinosaurs or geology.

The mastadon is really cool. I remember seeing it when I when there as a little kid in kindergarten or first grade.

This is one of the premier museums in the country for little kids to go to. Most are not all that into recent history or art. Stuff they see here will really make an impression because it is the stuff they are already in awe of.