Those look like "toad-poles". We have a marshy bog not to far behind or house, and we were OVERUN with
tiny toads this week. Kinda cute, but you have to watch everywhere you step-yikes....
Toad tadpoles are black, stay small and you end up with
teeny tiny toads (not much bigger than the tadpoles; frog tadpoles (the ones around here anyway) are green/brown and grow bigger and bigger untill they develop into small frogs.
Even though we have lots of tree frogs, wood frogs, etc. around here, I am not sure what those tadpoles look like.
Maybe you could capture a few of each and contain them until they mature. I'd love to see pics of that!