I have met with success in situations such as this by putting a young turtle in a separate container, such as a rubbermaid 3 gallon storage tote, put a small quantity of water in the container so that only a small pool forms in one corner, and then putting in one or two slow-moving but live food items. Wax worms or small slugs work well.
I make sure that the turtle sees the food.
Then, I place the lid on the container LOOSELY and step away for 10 minutes or so.

In this way, the turtle gets privacy, stimulation of moving food, and I can easily determine whether or not the food has been consumed.