Well, today I finally got a model rocket set ... been wanting one since I was about 8 years old. Now that my son is that old, I finally can justify it. :-) The kids and I went to a park and set up 4 launches (well really 3, more on that later) of a single stage Estes rocket (A3-4T engines, IIRC ... basically about the smallest engines typically sold.) Total cost was about $30.
The kids really enjoyed it, and I can tell by the questions Timothy is asking that he's thinking about implementation -- he's definitely got the budding mind of an engineer. (How does the ejection charge work? What's the purpose of the recovery streamer? How do multistage rockets work? Etc.)
We did have one minor mishap, on our first launch attempt. Turns out that the rocket had wedged against the small plastic keeper, creating just enough friction to turn our launch into a static test. The engine burned a small hole, about 50 mm in diameter, right through the aluminum guard plate on the launcher; an amazing testament to the power of even these relatively tiny rocket engines. Needless to say, it definitely helped demonstrate the importance of all the safety measures I was stressing. :-)
The next three flights went off without a hitch. The product documentation says "up to 350 feet", but I think the peak heights looked higher than that.
For his 9th birthday in November, I'll probably invest in some other more sophisticated models. Its cool to be a kid again, but its even more cool to see your kid's eyes light up; who knew learning could be such fun!