Chuck, my T-5R has the factory child seat but with 4 kids across various years needing various kinds of seats, I REALLY recommend the Kangaroo (brand name) style of seat for kids between 3-ish and, say, 7 (unless he/she's a tall 7). It has side bolsters the factory seat lacks, is wider and much more comfortable. Once you see a child trying to sleep in (or rather, on) the factory seat you'll see there is no comparison. And its cover is removeable (at least on the Kangaroo brand) and washable...NOT a minor feature! Also the child rides significantly lower, reducing injury potential more than a bit. The factory seat of course doubles as an arm rest when it's snapped shut, but that is a minor nicety as far as I'm concerned. Of course the 'Roo style can be moved from car to car (and airplane). Cost is under $100 - there are numerous brands like the 'Roo.
Don [T-5R and V70]