We purchased the Wenonah drop-in seat for our MNII which my daughter used when she was 5 & 6 years old. It does sit fairly high and kids always seem to be moving around, it did make Mom and Dad uncomfortable. For last year's trip we took her kid's camp chair (foldable) and set it in the bottom. It worked great and she sat much lower in the canoe. It is a much more reasonably priced alternative as well. We definitely recommend it.
Below are pictures of the drop-in seat and I didn't have one of the camp chair in the canoe, but you can see it sitting next to the canoe on a portage.