CUTE!
For a 5-12 year old it could be quite intimidating and confusing using the "proper" driving controls (where you have to accelerate or reverse to turn) but it was very nice for what it was.
Smooth (on medium quality anyway, slightly laggy on high as you said), nice graphics which would suit to the younger generation, and different tasks. Overall, a real nice solid game.
If i were to change one thing though... Be a bit easier on the children when they are driving into the grass! Instead of having invisible walls, maybe have the grass slow the cars speed to 1/4 of it's top speed, so the person playing can still turn on the grass and not get that horrible jagged/stuttering effect, yet would have to go on the roads in order to get the quickest times.
7/10