My Grandmother used to sing this to me back in the late Forties. What I remember is:

Twenty froggies went to school,
Down beside a rushy pool.
Twenty little coats of green, twenty vests so white and clean.

From there on I draw a blank until the last verse, to wit:

Now they sit on other logs,
Teaching othere baby frogs.

Any help would be gratly appreaciated, as I would like to teach it to my granddaughter.