If you have goldfish in the tank with these tiny turtles, they will starve to death, since the fish will eat everything. The turtles need to be in a tank by themselves at this size.
Did they come from a pet store? If so, it's illegal to sell turtles that size since most of them will not survive.
Go to the turtle forum I linked, and you can also read about proper care of these animals here:
http://www.anapsid.org/reslider.html