On this page, you can find a 4x4 board puzzle specifically designed for kids. Each block contains a 2x2 field, and it can be solved like a regular sudoku puzzle. This online game is free and works on smartphones too.
Once you've filled in all the fields, click the "I'm ready" button to check your work. Clicking the "new game" button will clear the numbers you've entered so far and give you a new board. The kid's sudoku board doesn't have a timer, it's not a competition, so play for the pleasure of the game!
Playing sudoku develops a kid's concentration and problem-solving abilities, as well as deepening their mathematical knowledge and developing logical thinking. If you're already good at 4x4 boards, you might want to try the easy sudoku.