The $29.99 all-metal desktop Stirling engine kit is one of the simplest. It can be assembled in 15 minutes and is recommended for ages 14 and up. Also for $29.99 is the Exploring Kid Steam Engine Kit.

“The Playz V8 Model Engine is a great kit for learning about engines,” said one shopper. “It's easy to build, fun to operate, and a perfect gift for anyone interested in engineering.

you could buy a mini engine kit and build a scaled-down example as the main feature of your coffee table. Many kits of varying complexity are available, and assembling one of these tiny engines ...