Hi Dan,
I can recommend Tortoises pretty highly if you're looking for low maintenance, but interesting pets. Before we met, my husband had a similar desire to have other living things around, but needed low maintenance pets due to his long work hours (and I think due to his extreme dislike of cleaning up, but he'll deny that). He purchased two Russian tortoises (Max and Shelley) and they have been wonderful pets for us. They are relatively small, won't get much larger than about 8-10" in diameter, and the children are fascinated by them. They have always lived outside, he built a "pen" of sorts outside using interlocking landscape rock walls filled with a foot or two of earth, a simple shelter, and a small circulating pond (he's an overachiever, a recessed drinking bowl would work just fine too). We feed them fresh vegetables daily, they take care of their business with very little cleanup, and the best part is that dig down into the ground and hibernate all winter! One word of caution: Properly cared for, our tortoises will live upwards of about 70 years. We'll probably be willing them to the children to keep in their own yard someday.
After 8 years, two kids, and two houses later, we now have a friggin menagerie! 2 Cats, 1 Dog, 2 tortoises, 1 Iguana, 2 mice, and a whole lot of fish later, we've lost the whole "low maintenance" desire, but still enjoy our tortoises.