Tadpoles are actually born with gills and after a few days a flap of skin covers them. You should still be able to see them if you look close enough though they will be very small.

Tadpoles need to breathe air just like us, but use gills instead of lungs. So there should be gill slits on a tadpole as long as it isn’t close to turning into a frog as which point it develops lungs, just like us.

The gills are on the side of the throat, behind the ears.

One step in a frog's life cycle is when the egg hatches and a tadpole comes out. This can happen anywhere between 6-21 days after fertilization. After about 4 weeks the tadpoles begin to grow gills, and then soon after the gills disappear. Tadpoles need gills because they are in the water, but adult frogs do not need them because adult frogs land animals.

Frogs develop from tadpoles slowly, over the course of several months or up to a year. The tadpoles have gills for different amounts of time depending on exactly what type of frog they will become. They will have gills once they hatch from eggs, and these gills will start to close up after 1-2 months. You'll notice that around that time, the tadpole starts to breathe by swimming to the water surface.