question is a little vauge, but basically the same way we do....
Animals that do not develop in a placenta will develop outside of the uterus rather than in. Kangaroos and Koalas use pouches to develop their young.
Ovoviviparous animals develop eggs but their young develop and "hatch" inside of their mother, so that the mother delivers live young.
example of develop inside the body of animals
they develop their young by laying eggs and teaching them to get food
Females have muscular organs called the uterus where the young develop during pregnancy. In some cases, such as in egg-laying animals, females have muscular organs like the oviducts that house and nourish the developing eggs before they are laid.
a young chicken develop because of the sperm cell and the egg cell
It's animal whose young develop in the mother's womb (such as in the case of mammals) and are born live, and not in an egg that hasn't hatched yet.
The kitten is very sleepy because it is a natural behavior for young animals to sleep a lot in order to grow and develop properly.
All animals feed their young.
There is a very simple sequence in which most animals develop. Most animals are born, mature, reproduce, and then die.
Mammals are the only animals that breastfeed their young.
oviparous animals live in more harsh environment and thus lay large number of eggs compared to viviparous animals. this high multiplication ensures that few of the eggs get fertilized (external fertilization) and develop into young once.