How I taught my 4 year olds to play
My son and daughter learned to play when they were 4 years old. Each learned at their own pace. We kept a board set up. They would sit down and want to play.
First we worked out how to set up the pieces, then how to move the pieces. While they were learning that, they learned the two rook checkmate. Once they knew that, I took off all my pieces and we played all their pieces against my king.
We worked on getting all the pieces out in the opening (unchallenged) and moving the king to safety. As they got better, I added pieces. It's nice having a game we can always play.
There's no forcing it, though. When they were ready to play, they played. Until then we just made up games on the chessboard and enjoyed each other's company.