Not sure if it would be suitable for a 10yo, but check out MHRD (on steam or itch.io), you start out with NAND gates and gradually build more complex constructs that you reuse in the following levels, where the final level is a (very simple) CPU. Sort of like the first few parts of Nand2Tetris.
It uses a very simple HDL, has a reasonable IDE built in, and each puzzle is pass/fail based on a test suite so it's easy to get into - however, you only have a certain number of lines on screen in which to write the HDL (and comments), so brute force is not an option for most of the puzzles, you do have to optimise your design to fit the constraints.
It uses a very simple HDL, has a reasonable IDE built in, and each puzzle is pass/fail based on a test suite so it's easy to get into - however, you only have a certain number of lines on screen in which to write the HDL (and comments), so brute force is not an option for most of the puzzles, you do have to optimise your design to fit the constraints.