I hate to put a downer on this but Thumbelina is a dwarf miniature and there is a lot of controversy esp in the US about the breeding of miniature horses predisposed/carrying the dwarf gene. It causes all sorts of health issues for the ponies and high mortality rates.
"Many brachiocephalic dwarfs suffer from crooked legs and numerous orthopedic malformations. In some cases corrective farrier work can be performed using glued hoof extensions to force the dwarf to stand flat. In other cases, surgery is required to correct leg deformities. These surgeries might include: Contracted tendons , Locking stifles , Shoulder dysplasia. Many also suffer from restricted breathing and painful arthritis."
Accidents do happen but I think its highly irresoponsible for breeders to knowingly breed from ponies with this condition in their lines.
http://www.mini-horse.org/menu_dwarfism.html