Sorry this is late but I was out of town for a few days. I'm from that area originally but only really have experience with Rebounders which is an incredible gym. They have up to level 9s right now but have had some 10s in the past on the girls side. They also have a great boys team that has landed tons of guys on very respectable college gym teams. I do know the former boys head coach recently left to start his own gym though, Ultimate Gymnastics which is also in Baltimore. He's a great coach, but I don't know anything about his new program. They offer boys and girls teams though and it could be a possibility. The gym is very new though so the program is not as well developed as others in the Baltimore area.
There is also United Gymnastix which I don't think has been mentioned before in this thread. They have a boys and girls team. There is also Barlow's in Annapolis.
First Class, Top Flight, Columbia, and Docksiders all have boys and girls teams as well. But these gyms are stretched over a pretty big area so it really depends on where in the area the family is moving to and how far they want to travel. Rebounders and United are more on the Northern end of Baltimore. First Class, Docksiders, and Barlow's are in the Annapolis area. Top Flight and Columbia are kind of South West and a little closer to Gaithersburg, Rockville, and the other DC suburbs. Hope this helps a little!