Let me add another of my 2cents
Don't loose focus.
There's been a lot of interesting input given here, but if your "contraption" is intended for kids, keep it simple.
Adding to much information or a big board... may be overwhelming for kids (starters) and demotivating.
Keep your tiles simple. But, adding to that I suggest that you write a small book with simple instructions and experiments, with schematics, some introduction to functions. On some, instigate the curiosity proposing alternate ways to achieve the same results, or add a slight complexity to it, for instance, making a mix with 2 previous experiences or something.
The building blocks should be simple and easy to read and understand, because that will be easier to visual memory, to build the circuit and to debug if necessary.
The extra information should be provided in the book, and increased as necessary.
Keep up the good work
