Hubby uses the Touch mostly, and he likes it. Yes, the Kobo Touch does use the Pearl e-ink screen. My experience with the Kindle and Sony screens are extremely limited (just seen over someone's shoulder on the bus or in a display in the shops), so I can't compare based on real life usage experience. And anyway, I might not be the best person to ask about screens; I don't even mind my old Aluratek screen.
If you're looking for something not overly expensive, the new Kobo mini (5 inch screen, the specs aren't clear if it's Pearl?) has just come out. I think I heard that WHSmith was carrying the Kobos in the UK, so they might have demo models that you could check out and see if you and your little boy like the screen.