Welcome to Science Buddies! It's nice that you are interested in learning more about your pet turtles.
Since they are young turtles, you could look at how a factor like temperature affects their growth rate. For example, you could keep each turtle in the same tank for a while to monitor their growth rates at the same temperature (as a control), and then move each one to a different temperature (one a bit colder and one a bit warmer, for example) to see whether their growth rates increase or decrease. If you are interested in something along these lines, let me know, and I can help you design your experiment.
If you have other kinds of pets, you might be interested in this Science Buddies project, which compares how different animals eat: http://www.sciencebuddies.org/science-f ... p029.shtml
Note that ectotherms (cold-blooded animals) like your turtles tend to have lower energy requirements compared to endotherms (warm-blooded animals) like cats and dogs. So if you have other pets, I think this would be a good project for you!
Did you know that migratory turtles are thought to sense the Earth's magnetic field? Check out this Science Buddies project: http://www.sciencebuddies.org/science-f ... p058.shtml
I do not think that eastern box turtles are migratory, but this might be an interesting animal-based project for you. You might be able to find a way to test whether your turtles can sense a magnetic field (even though they're not migratory)! Let me know if this sounds interesting to you.
I hope these ideas help you get started. Please post again (in this same thread) with what interests you, and we'll go from there!