No particular system to recommend, but another suggestion.
The player's starting position is like a baserunner, not a sprinter, correct? Many kids have their weight evenly distributed over their legs, and their feet in a square stance. It is not cheating to have the weight loaded on the front (right) leg and the feet in a slightly open stance. This can help the back (left) leg come through with a quicker and more powerful first crossover step.
Don't trust me, time it for yourself. First with the even-weight, square stance, and then with the front-loaded weight, open stance.
EDIT: I've seen it worth .1-.15 seconds. Each kid's mileage will vary