I decided to use the cuban coin decoration to make my educated guess to your question.
The reasons being that: 1) The cuban coin is roughly the same size as a frog, and 2) unlike most decorations, the cuban coin does not have much size variation. Since natural decorations such as flowers, leaves and megalodon teeth can significantly vary in size between individuals, they could lead to errors in calculation.
After a bit of research, I found that the Cuban coin decoration is modeled after a 20-centieme coin. These particular coins are usually about 23mm (~0.9 inches) in diameter. So, assuming that the frogs are the same size as the coin, they would be about 9/10 of an inch long, which is not very large if you think about it.
