Many adult birds are easy to identify, especially the cardinal, with its bright red feathers and distinctive plume. The babies, however, might not be so easy to tell apart. Baby cardinals do not exhibit many of the same distinctive traits as the adults, but they do have a few unique characteristics that set them apart from other baby birds.
Look at the birds while they are still in the nest. Cardinals are born with pink skin and gray scales; once they begin to molt, their feathers will come out a tan color. Baby cardinals also have uniquely large, beady eyes. They will have a large eye socket not unlike many lizards. A baby cardinal's mouth is red on the inside, and it will often lick its beak.
Watch for when the birds begin to leave the nest. If you know what day the birds first hatched, you can identify the cardinals because they will likely be leaving the nest after nine or 10 days, while many other common birds, such as robins, sparrows, wren and pigeons will take up to two weeks or more.
Watch the bird as it grows. Once a baby cardinal has left the nest, it will still be the same tan color, but will be growing the distinctive cardinal plume. On a baby, this will appear as a small tuft of feathers that grow straight up on the middle of its forehead.