One of the tadpoles is now a frog but i have no idea about what to feed it.

try fruit flies or wingless fruitflies for a few months untill they are big enugh for flies

i used to catch small house flies for mine. i had to pull a wing off so it couldn't fly as the frogs couldn't catch them.

so no longer a fly more like a walk

The NZ frog book I have states "frogs will eat anything that moves as long as it looks like it fits in their mouth". Also variety the key and can die eating food too big. Spiders and moths are good. Also says worms, crickets, grass hoppers etc etc. Not Monarch or Magpie moths or caterpillars as are poisonous. Suggests scooping a net under some leaf litter to get any creepie crawlies. Pet shops have those containers that hatch flies and things out over a period of time. My brother goes around the house last thing at night getting any sleepy moths, daddy long legs etc. Obviously need to start with small ones or remove bits to make it small. I had several for about 12 yrs until a friend accidently cooked mine in the sun....very sad!

Don't give them spiders as they can bite the froggies. I used to give my whistlers flies I caught myself in summer and petshop flies in winter. If you keep the container in your fridge (if Mum will let you) they hatch slower or hot water cylinder cupboard to hatch faster.