We use Dr. Reardon in Arlington (closest to Ballston metro), here:
http://www.drreardon.com/ . We started with her because she made an effort to go visit the pre-k classes in our daycare and to talk with the kids about oral health and my kids always talked about how fun her visits were. My boys (both ADHD, one with significant anxiety) have been going to her for years now, and she and her staff always handle things well with them. She is co-located with a dentist who sees adults (Dr. Williams) and I see Dr. Williams for myself, I think it helps my boys to see that we all go to the same dentist office.