First game against Mini-Me

I have a 4 year old son who has become curious about chess. During the past six months or so, he has learned how to play with just the pawns and kings, and also how to set up the board and how to move the pieces.

A few weeks ago, he and I played our first game with all the pieces. I have to confess that I did not play my best against him, but he played all the moves by himself without my help. That is, up to the final position. He does not yet understand the concept of checkmate, so I had to help him to find the way to conclude the game.

After the move 30. Kg7, white has a forced win. Can you find it?