What are you feeding the tadpoles? Unlike most tadpoles, which are exclusively herbivores , spadefoot tadpoles are omnivores. They also eat dead insects and tadpoles, as well as fairy shrimp.

If they haven't come out of the water yet they'll probally still eat fish food/flakes. Maybe try some small frozen (unfroze) blood worms dropped into the water in pieces, or dead/alive tiny brine shrimp (sea monkies). The last might simulate something they'd find in the wild as fairy shrimp are tiny as well. \

Any pet store should have brine shimp, frozen and usually live. I'd try both.