I was going to comment why not get them an iPad, but that would be a big change all at once. I like your approach of slowly introducing them to the new software they'd be running on Ubuntu on their Windows 10 system. That way they get used to all the new programs and the final switch to Ubuntu is pretty much a non-event. Smart! So smart that I don't think transitioning them to an iPad would be that easy.
I’m not an Apple fanboy by any means, but the reality is that a lot of people don’t need a PC or Laptop of any sort, they just need an iPad!