Great question, and luckily the answer is NO! Polliwogs or tadpoles do not need air to breath. They have gills like a fish and get oxygen from the water like a fish. As long as there is still liquid water underneath the frozen surface of the pond, the tadpoles will be fine. Frogs on the other hand do need air to breathe. When the cold months come and their homes are frozen over, many frogs that live in water will hibernate or sleep to save energy. During hibernation these frogs do not need to breathe as much so they can get enough oxygen from the water to survive the winter. Frogs that live on land will dig little holes in the dirt and hibernate there until it gets warmer. When the tadpoles turn into frogs they will know what to do to survive. Frogs are used to living in very cold places, so there is no need to worry!