have an outer body covering of hair / fur.

produce milk to feed their young.

breathe atmospheric air using their lungs.

most mammals give birth to their young alive. Some special mammals like platypus and spiny anteaters lay eggs.

most are warm-blooded (maintains a constant body temperature)

human, bear, bat, whale and dolphin are some examples of mammals.

have an outer body covering of feathers.

have a beak, a pair of wings and a pair of legs.

reproduce by laying eggs (hard shell).

most bird have the ability to fly. Some special birds like penguin, ostrich and emu cannot fly.

warm-blooded

chicken, peacock and parrot are some examples of birds.

use gills to breathe, taking in dissolved oxygen from the water.

have an outer body covering of scales.

most fish reproduce by laying eggs. Some special fish like swordtail fish and guppies give birth to their young alive.

cold-blooded (body temperature changes with the surrounding temperature)

shark, salmon and tuna are some examples of fish.

have 6 legs.

have 3 body parts: head (with feelers), thorax and abdomen.

have a hard outer covering called the exoskeleton. 
They moult in order to grow larger.

cold-blooded

grasshopper, ant and mosquito are some examples of insects.

have dry skin covered with scales.

breathe using lungs.

reproduce by laying eggs that have a leathery shell.

cold-blooded

lizard, snake, turtle and crocodile are some examples of reptiles.

lay eggs with jelly-like covering in water; young live in water.

the young of amphibians take in dissolved oxygen from the water using gills.

adult amphibians live on land and can breathe atmospheric air using both moist skin and lungs.
They can also take in dissolved oxygen in the water through the moist skin.

cold-blooded

frog, toad and salamander are some examples of amphibians.