The fictitious country of "Ptomania" is a play on Ptomaine poisoning, then in recent memory a real problem with tinned food.
Lupino Lane is pursued on Blackpool beach by enemy agents. He mounts a horse and they mount donkeys (that were offered for children to ride on the beach.) In the chase that follows the soundtrack is from the Overture "William Tell".
The youngest of the five step-children is clearly played by a young adult male of small stature. Possibly about 2 ft/60 cm in height.