[QUOTE=zippyrider;7849093]
Is there any safety argument with having a child on a larger pony? [/QUOTE] If anything, the larger may be safer.
[QUOTE=zippyrider;7849093] In other words, is the 4" difference in height between a 14h and 13h pony, for example, a safety concern (in the event of a fall)?[/QUOTE] Nope. That is a myth. 4" is not going to dramatically increase the impact of a fall. With the right pony, regardless of height, kiddo will have fewer falls.
As others have mentioned, a larger pony usually has smoother strides which might mean less bouncing off. An adult can hop on a larger pony if “pony tude” rears its head. That is a safety benefit.
[QUOTE=zippyrider;7849093] Is there any legitimate argument that it is easier for a child to learn to canter or jump on a smaller pony?
[/QUOTE] Nope. As others have mentioned, larger ponies usually have better gaits. That makes them easier to sit.