1984 Specialized Stumpjumper Sport 24" wheel:

Most of the early mountain bikes were made in pretty large frames.  Often, they were available in 19", 21" and 23" which is huge by today's standards.  One way of offering a smaller frame was to use 24" wheels with a 17" frame.  These bikes weren't necessarily kids bikes but sized for smaller adults.  You can see that this bike uses pretty much identical parts to the same model full-size bike.

Sugino crank, check out the rear wheel clearance!	Neat Biplane Style fork crown, Tri Cross tires	Nicely lugged frame with steel Specialized headset