My baby aquatic turtles only eat the dried baby food i offer them? why is this and how can i get them to vary?

i tried tomatoes, little fish, lettuce, earthworms, even cauliflower! one turtle will eat absolutely anything! yet the other 2 only eat the dried baby turtle food. Their constantly begging for food, yet always for their favourite. I want them to eat other foods...its apparently very important for their health.