Yes. For those born with the ability, bending shows up at some point in childhood. Usually no later than the age of eight, but often earlier. Fortunately, it's much weaker in childhood than in adulthood...although that didn't stop me from being a little terror in snowball fights as a boy.

[He doesn't have a lot of great childhood memories associate with bending, but being a waterbender kid in a snowball fight was always pretty great. He'll never deny that.]