Uh-oh, when I wrote up the springjack, I limited it to riders of Small size or Smaller figuring that the kithkin would be Small. I can change that, BUT I think there are more sources state that kithkin should be Small rather than Medium sized.
Here is a quote from http://tvtropes.org/pmwiki/pmwiki.ph...sAreAllTheSame
[T]he kithkin in Lorwyn were portrayed as sort of a cross between hobbits (which is what they were originally intended to be called) and dwarves, combining the Little Folk's general smallness and pastoral living with the Stout Folk's tenacity and well-organized communal defense; the kithkin become even more dwarflike in Shadowmoor, where they have abandoned their country villages for heavily fortified castles and become rabidly xenophobic.
Of course, they couldn't be called hobbits because the Tolkien estate has that as Intellectual Property. However, they remind me of 2nd edition halflings, which were plumper and had hairy feet. Kithkin don't have hairy feet but they are stockier than halfliings.
Dwarves are 4 feet tall. That is the maximum height for Small creatures and the minimum height for Medium creatures. I don't think the kithkin should be taller than dwarves in any case. They are like a dwarf-halfling hybrid and that would make them Small.
Don't worry about your spelling; we can help with that if you want. My Inglés a Español spell is even worse.
Debby