I have a soon-to-be-4. Is touchscreen a must? I'm not sure he will be very good with mice or trackpads.
Touchscreen seems to be easiest be it for playing games or navigating youtube. He uses google voice quite a bit on an Android smart phone, since he found the "mic" button.
I have a 23-inch touch monitor hooked up to an intel nuc with Win10, which he seems to like a lot. Though the educational apps in windows store are very few. I was not able to find a way to hook up an Android variant to the touch monitor.