Tadpole question

I have a small plastic pond in which a frog laid a zillion eggs. Up
until a day or so ago, I had a zillion tadpoles, all of whom happily
snacked on the algae. I noticed a week or so ago their back legs had
sprouted (or whatever you call it when back legs suddenly appear). Two
days ago there was nary a tadpole in the pond. They were the size of
large peppercorns. Could they have left the pond or did something kill
them all off? I really miss them. I'd go look at them every day. :^(

Peg in Charlottesville, Va