Cats are the second most popular pet in the world after dogs, with more than a quarter of households in the United States owning at least one, according to the U.S. Pet Ownership & Demographics Sourcebook.
Most of them are acquired when they are still kittens, which are cute but require more care than adult cats.
Here are some things you need to know about looking after kittens.
How Much Do Kittens Sleep?
New kittens are quite like newborn babies in that they need to sleep for much more time each day than the average adult cat.
Newborn kittens sleep around 90 percent of the time, accounting for around 22 hours a day, according to pet food company Purina. As they mature, they will need less sleep— an average cat sleeps between 13 and 16 hours a day, roughly twice the amount a human requires.
"Kittens are babies and just like human babies they need plenty of sleep and round-the-clock care," Anita Kelsey, feline behaviorist and author of the new book Let's Talk About Cats, told Newsweek.

"They are being cared for by their mothers—this includes getting warmth from their fur and bodies. They have not developed yet and so they are pretty dependent on their mothers for health and care until their senses have developed. Kittens, just like human babies, get tired very easily and do fall asleep in the most unusual positions."
"Kittens sleep a lot, between periods of frantic activity! From birth they can sense warmth and have a sense of smell. These guide them to their mother's belly. Between 2—16 days, their eyes open and their vision slowly improves," added Celia Haddon, a cat expert and author of A Cat's Guide to Humans.
What Shots Do Kittens Need?
Kittens need to have injections when young to make them immune from diseases.
"All kittens should receive a course of two primary vaccinations at around 9 and 12 weeks, this coincides with their immunity from their mother's milk falling," Rosemary Fisher, director of the Governing Council of the Cat Fancy (GCCF), told Newsweek. The GCCF is the leading registration body for cats in Britain.
"Kittens need protection against diseases common to cats and since they are new to this world they are vulnerable to picking up diseases and parasites. The main three vaccinations a kitten needs to get are: Cat flu, Feline panleukopenia virus (FPV) and Feline leukemia virus (FeLV)," Kelsey added.

When Do Kitten's Eyes Open?
Kittens are born with their eyes closed, their ears are folded and they can't stand up.
"A kitten will start opening their eyes anywhere from 7-10 days although this could be slightly longer. Cats are a species blessed with two eyes and it's a natural part of this species' development to open them," Kelsey said.
"Their capacity to focus with both eyes is around the third week. They begin to respond to sound by orientating themselves towards it or away from it from about day seven onwards and they can locate the direction of sound at about day 16," Haddon added.
When Do Kittens Start Walking?
Most kittens start walking at around three weeks of age, according to cat advocacy group Alley Cat, and their teeth will be coming in too. The group says this is the time that the owner should start providing a litter box and wet food.
"Kittens move around in the box from birth, but tend to stay close to their mother. By two weeks they are crawling and by four weeks they are quite active, play fighting with each other and trying to climb out of the kittening box. Once out of confinement, they become very active and by 6 weeks are investigating their surroundings and trying to climb," Fisher added.