not bad!
Not a bad child's matching game. However, my biggest criticism is the lack of control in difficulty. While you claim the difficulty is easy, starting out with 16 cards is perhaps too much at first. It would have been nicer to start with 4, then move to 6, etc.
Nice selection of horses, although some pictures are very similar. Adding difficult colored borders for each different picture would also help the child make the connection as well.
Congrats on making your first game!