Simon Tatham’s Portable Puzzle Collection is a great collection of free Java logic games. Here, you can find challenging games such as Black Box, Bridges, Dominosa, Guess (also known as Mastermind), Inertia, Mines, Magnets, Untangle and many more. All games are easy to learn and difficult to master and will develop a kid’s logical thinking.

The site is completely ad-free. The C and Java source code is available for download, and you can publish the games on your own website if you want to.
Playing a logic puzzle game called Cube on http://www.chiark.greenend.org.uk/~sgtatham/puzzles/.