It's a pretty nice kids game. Sometimes the flies don't get destroyed because they're not overlapping the target so either make the target bigger or make the flies hit box bigger. Also the number hangs around after you destroy the fly because of the "System:Wait 1 seconds" so you'd want to destroy the number first.
Maybe add some different end text depending on the player's score. "Congratulations! You got 0 correct!" Sarcasm? <img src="smileys/smiley36.gif" border="0" align="middle" />
I have to say I find the constant buzzing annoying though.