I guess some of that depends upon where you are, and what discipline you want. Western is pretty hard to come by, but there is one place in Berryville I personally love, and they have their own small kids and would probably be great. Most of the rest is H/J or dressage that I am aware of, and I do not know any of them (in MD I could help you.....)I would recommend looking here:Virginia Equestrian.com
And going, visiting, seeing who is close, who you think you can get along with, etc. Your girls are very young, and some places may not deal with that age, would be my guess.