My great great grandpa taught it to me as follows:

Down beside the rushy pool
20 froggies went to school
20 little coats of green
20 vests all white and clean

Mr. Bullfrog on a log
taught them how to say " KERCHOG"
taugh them how to dodge the blows
from the sticks the bad boys throws

20 froggies grew up fast
bullfrogs they became at last
now the sit on other logs
teaching other little frogs.

Its possible that his mother who immigrated from ireland to indiana around the early 1890s heard the poem and mis-recited it, but this is the version my family has sung to every generation of children since then.