I appreciate this information as well. Scrkpr, your original post interested me because my nephew is four and while he's not quite at the level of your son regarding knowledge of astronomy, he's clearly very bright, and he enjoys the time I spend teaching him about the planets. One day, I told my sister-in-law that I read on an astronomy board online about a four-year-old who has been asking for a telescope for six months. My nephew heard, and then he asked for one! None of us in the family has one, but we have discussed the possibility of getting one for the family to share, as we all live in the same town. So the information in this thread may prove useful to us as well as to you.