Can you post a bigger/clearer picture?
They really need deeper water. I'm not quite sure what you mean by a play area. What a lot of us do is build an above tank basking area - ours are three pieces of Perspex, two nearly the length of the tank and the third the width. These are then screwed to wooden battens and it "sits" on the inside ledge of the tank. This means the tank, which must be well supported, can be filled virtually to the top. Obviously the turtles must not be able to climb out or reach the lights.
What sort of light/basking area do yo have?
As for diet - not exactly sure what baked mealworms are, but you want to be feeding a good quality pellet such as Reptomin and pondweed, duckweed etc.
This should help:
Terrapin Information UK
Welcome to the Forum but you may want to repost in the main Shelled section where a lot more people will see it.
Do ask if anything isn't clear.