[jerluc]

I've been building a very simple development "portable" PC using a 7" TFT display, wireless keyboard, and a Raspberry Pi. At the moment, it just boots into a Linux login shell, but you can program it to boot into a desktop environment if you want (and if you have the power luxuries!). Of course, the Linux environment may be too much for kids, but this might be close to what you want. Also a decent overall price: altogether so far, I've paid a little less than $100 for this whole setup ($30 for the display, $35 for the RPi, $25 for the keyboard), though you could get it for much cheaper using a Raspberry Pi Zero ($5!) and a cheaper keyboard.