Instead of expensive protein drinks, just give them some milk if they have the ability to break down lactose. Choco milk is alright, but has about 2.5 times as much sugar as nonfat to whole milk. So I wouldn't drink massive amounts of choco milk, but regular milk is fine. Choco milk is also good for replenishment as it has a fair amount of carbs besides protein and fat.
Honestly, the USRDA of protein is atrociously low for most athletes of any kind, especially gymnasts. It's ok for the normal everyday person who is weak( national average of 1 pullup ). Ideally, gymnasts should be intaking no less than 0.7g to above 1g of protein per pound. It is a real pain in the butt to get many girls near this, especially as they get older.
To gain mass, especially muscular mass requires being in a positive intake of calories per day and lots of protein besides hormonal stress during intense exercise ( BW or weightlifting ). No, bike riding and running don't really count if they are in the endurance scope.
Btw, no soy protein. For either young boys or girls.
If they can't do dairy, try eggs. If they can't do casein, do meat. If they don't do meat or fish, umm eat ridiculous amounts of veggie protein that Ross Enamait reccomends
http://www.rosstraining.com
While IMO, most young male gymnasts probably eat enough, especially protein, most female gymnasts do not; though the little ones have better eating habits than the older ones.
I wouldn't bother with many doctors but look into a sports oriented nutrionist. Especially one experienced with power (anaerobic ) athletes.