Why are dolphins and whales called mammals even they swim like

Whales are mammals because they give birth to live young, they have fur (although it is very sparse on their body), they have lungs and breath air and they provide milk for their young

Explanation:

Well...its cuz of the characteristics of mammals(give birth-not eggs, they have fur, are warm-blooded; the young are fed milk produced by the mother's mammary glands)

Explanation:

Whales and dolphins are called mammals because they give birth to live young, they have fur, they have lungs and breath air and they provide milk for their young.

Hope this helps:)