interfacing buttons with python/c++
People who told you they don't exist sorta lied.

What you will need:


The cheapest mouse you can find. Really, the cheapest.
Your Big Easy To Use Whatever You Need buttons. Grab an SPDT type.
Some fancy tripolar cable to connect them, grab the size and color you like
A soldering iron, and somebody able to use it


First of all, crack open your mouse. You will see something like this:


By Job at English Wikipedia - Transferred from&nbsp;en.wikipedia&nbsp;to Commons&nbsp;by&nbsp;Ansumang&nbsp;using CommonsHelper., GFDL, Link

See those tiny little guys on the right, with red little thingies on top? These are microswitches, something like this:


By Benjamin D. Esham / Wikimedia Commons, CC BY-SA 3.0 us, Link
without the metal thing on top. The red thingies correspond to the black piece of plastic on the top left of the switch case.

You now need to identify the terminals of the switch. Odds are that they are labeled as C or COM, NO and NC, as COMmon, Normally Opened, Normally Closed.

Now you need to start soldering. Your Buttons will have three similarly labeled terminals: you need to remove the switches and solder your cables where the switches used to be, then solder the cables to the terminals on your buttons. Really, it's easier said than done.

Finally, enjoy making your rig nice and all so that a young human fancies using it and is not endangered by anything.

And... Bingo. You're done.

Now, this is not really useful to you, in the sense that you do not learn much. But this solution has many pros: it is dirty cheap, easy for you to interface to, no worries about safety for the youngsters, great flexibility, you name it.