Cherubs and crocodiles must be a fairly common motif; here's another example in Dumfries - several actually, around an incredibly brightly painted fountain:
There must be some symbolism attached, but who knows. Maybe something to do with innocence controlling animal power, or somesuch? It might also be that the Victorians were just borrowing an older usage, without worrying much about its meaning (assuming these are all 19th century).
All the world seems in tune on a Spring afternoon, when we're poisoning pigeons in the park.