You are probably feeding them too much. By the time a turtle hits 4 inches, it's not really a juvenile any more.
In the wild, the diet of a young turtle is mostly protein from tadpoles, crayfish, snails, etc... There have been scientific studies which show that as a RES ages it becomes more and more vegetarian--to the point where a very old turtle may get less than 10% of it's diet from animal sources.
When a turtle is young, less than 4 inches, the recommendation here is enough pellets to fill its head once a day, with the gradual introduction of more vegetable matter. By the time it hits 4 inches, the recommendation is vegetables every day and pellets every other day or even less.
The nutritional section of the main site has lots more information:
http://www.redearslider.com/nutritional_content.htmlIn particular, look at the sections on pellets and fresh plants. The Pyramiding section of
http://www.redearslider.com/shell_conditions.htmltalks about some of the dangers of overfeeding.
Can you post pictures of your turtles?