Like all mammals, baby bats drink mother's milk.

More Info: Baby bats, called pups, are nursed on their mother's milk from birth up to six months.  During this time, the mother bat will teach her pup how to fly and search for food.

How Do Bats Reproduce?

Female bats possess the extraordinary ability to delay fertilization or egg implantation based on the availability of food or other environmental factors.  For many species, mating occurs in fall directly preceding hibernation.  The body of the female bat is able to store the male sperm until she wakes from hibernation in the spring.  She will generally give birth in the late spring or early summer.  Some species, such as the common fruit bat, have been observed to synchronize births within groups.  

(Kalko, Elisabeth K. V., and Ph.D.. "Great Ideas in Science - Mammal Directory." Rainforest Connection. N.p., n.d. Web. 26 Sept. 2011.)

How Many Babies Do Bats Have?

Most bat species have one baby at a time per season.  Bats, like other mammals, are attached to their young and can recognize them through scent and sound.  A mother bat will nurse her baby and provide it protection as it is born with undeveloped wings and cannot care for itself.  She will nurse and care for her baby from birth up to six months depending on the species at which time the bat is nearly full grown.