I think that the Fairfax County parks and rec offer camps during that "private school" spring break. You could check on their website (just google Fairfax County parktakes and do a search on their camps). You may be able to find one in FFX County Alexandria or otherwise near a Metro.

Any information on camps for 6 year old in Alexandria, Arlington or DC, close to metro? I've been looking into The Theater Lab at the School of the Dramatic Arts but can't find no reviews on it, thus far.
Thanks,
Indira