Here's a perfect saddle for youngsters! The Ghost Mini has the base and integrated pad of the Bareback Pad models (Mandriana, Toscana, etc) but a seat styled after the standard Ghost models. And it's 30cm (12") from pommel to cantle - compared to 15" for the same measurement on the bambini (16") models, so 3" smaller!
The stirrup hanger is velcro so can be adjusted as your child grows.
For an even smaller, super secure saddle for toddlers, check out the Buttera Vittorio which will be available soon.