Digital logic resources for youth

My son (11) has recently become quite interested in digital logic - designing adders and multipliers based on logic gates. So far he's mostly done this in minecraft with redstone or on paper. It works okay, but it is somewhat limiting. He'd like to understand how to design a full simplified computer. This is far from my area of expertise.

- Are there good books on the subject for kids his age? I think he (and I) would be okay with a big text book, but introductory texts or projects might work better. At least something that introduces the major components and how they function and interact. - What are good simulators which would allow this to be created and visualized? I'm not totally opposed to doing this with physical electronic components, but a simulator feels like it would be simpler.

In my searching I wasn't able to find a happy medium between full professional digital design and super simple digital logic introduction, but missing the creation of all components of a simple computer. Thanks for the help.