Let's Build Something for Toddler(Edu+Music)

Hi all, I would like to have a project building a some kind of basic/tangible toy for toddler age(2-5 year olds). These little users are the best people to deal with employing the real/tangible stuff that they can play with hands.

I don't have a solid idea yet, but I have a couple of things in mind.

Building blocks which give sound rewards for building up well. For example, as the toddler build something higher than record he has before, he will be rewarded with exciting music or LED blinking.

The other one was a squishy ball remembers movement (this can incorporated with music beat as rhythm learning tool).

*Added*

Natural Musical table - I am thinking of two versions of this; one with sand/marble or one with surface of scribble/drawing

Just like how orgel/music box works, kids can play and make whatever shape or structure on table, and the music will reflect from what's build on. In this way, they can have fun while they are playing and learn little bits of how rhythm or pitch works. I think this can't be very hard to build and it will be a lot of fun.

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More ideas are coming since I have a toddler-aged son myself. 

I don't have solid background on electronics or programming, but I am a fast learner and also have a very reliable source(my significant other) who has solid background in these kinds of stuff. 

If there is anyone with more ideas or interests on building these kinds of things, please comment on this or contact me to kmpark@ischool.berkeley.edu