[janoskiss (Steve H)]

4.5" Dob would be great for a little one. 6 or 8" for bigger kids. I'd say 4.5" for a 7 y.o. but they seem to be hard to get for reasonable cost. AZ3 mounted refractor, e.g. 80mm from http://www.aoe.com.au/refractors.html , is not too shabby either.