Many people who work with cats and kittens will tell you that it is better to adopt two kittens instead of one. There are probably a hundred good reasons why this is true, but here are my top 5:
One kitten can become lonely
A kitten left alone during the day can become lonely and bored, which sometimes can lead to mischief. Two kittens will never be lonely, especially if they are siblings. In fact, you'll often find situations in shelters and rescue group adoption where a cage will contain two kittens with a sign, "These kittens may be adopted only as a pair." Shelter volunteers recognize that siblings really need to stay together. And since shelters are often frightening, unfriendly places to small creatures, unrelated cats often form close bonds that should be respected when adoption time comes.
One kitten can just drive an older cat nuts
Although it might sound contrary, an older, established cat will probably accept two kittens better than one. One kitten will seek out the older cat as a playmate, or worse, tease and pester the senior cat which can cause stress to an older cat. The kitten in return, will be "rewarded" for his playful efforts with hisses and swats. Two kittens will expend their energy in play with each other, leaving their older "uncle" to relax in peace.
They help each other burn off energy.
Even the most devoted human caregiver can quickly become exhausted by trying to keep up with the energy of a single kitten. Two kittens will wear each other out, leaving their human parent free to just enjoy watching them.
Fewer behavior problems with two kittens
Many people who experience behavior problems with kittens find that some of them go away when they adopt another playmate. What may be perceived as mischief is often just the result of boredom. Much like their human counterparts, kittens sometimes misbehave because "negative attention is better than no attention."
They will each have a friend for life.
Two kittens who grow up together will almost always be lifelong friends. Although they will sometimes have their little squabbles (what friends don't?) you will more often see them engaging in mutual grooming, playing together, and sleeping with their best pal. If you are considering adopting a kitten, think about your best friend and consider whether you would deprive your kitten of the enrichment a friend brings to life.