I also have 2 little ones, Paisley is only 12" at the withers and Isla just scraped into small and has to be measured again so I'm hoping she gets to stay in small! Merfyn is a little taller (not by much) so I'm guessing he will be in medium, but I'm happy that he will be capable of jumping that height.....I don't think the Isla would manage it, not for a whole course anyway!