Back when I was in grade school, I found that I could type much faster than I could write, and I also found that typing was less exhausting. Because of this, for much of my school career, I was allowed to type my assignments and exams rather than writing them. I believe that I first learned to type when I was in 3rd grade, and I started typing assignments on a somewhat regular basis some time around 4th or 5th grade.
If you get your child a tablet, make sure it can support some sort of an external keyboard with physical keys. Better yet, get them an actual laptop, as they come with physical keyboards by default, and unlike tablets they are actually designed for content creation, not just content consumption, so they can utilize things like printers, external storage devices like USB drives and writable CDs, and of course much more fully-featured software.