For a game being marketed to kids, it is good, the mouse cursor is a bit sluggish, the SFX do get a bit boring to listen to after a while, and the background does get a bit stale after a while, but overall it is a nice game. (also you got my hopes up a bit with the pictures as I thought it was a connect 4 type of game rather than tic-tac-toe)

I like you colorful candy-like art style! The  music, soundFX and voice acting blends perfectly well with this style.  The individual colors and backgrounds for each character is also a great idea. The UI is easy to grasp and does a good job as well.

The only improvmeent that comes to my mind: The mouse cursor is feeling too sluggish. It lags significantly and follows my movements too slowly.  If your game engine offers a  OS-system based custom cursor option, I would suggest picking this one instead.  The tradeoff might be a smaller picture, so I am not sure how important you think the big cursor size is for your game and audience.

Overall nice game, the endless matches could be a good thing to keep kids occupied for a while. The AI gives the player chances and can outsmart the player, perfect difficulty.

This is true. The art style is also fine.

Fits children theme: Yes
Fits Doraemon: Yeah, the characters are recognizable

Overall nice game, the endless matches could be a good thing to keep kids occupied for a while. The AI gives the player chances and can outsmart the player, perfect difficulty.

The game ran slowly on my laptop which shouldn't happen with a simple game like this. I'd say around 3-5 FPS. Optimization is really needed. I doubt it's the code, it's probably the engine.