It’s a myth that parent birds will abandon young that have been touched by humans–most birds have a poor sense of smell, and birds in general identify their young using the same cues we humans do–appearance and sound. It’s perfectly safe to pick up a fallen nestling and put it back in the nest, or to carry a fledgling out of danger and place it in a tree or shrub. But please refer to the question on what to do if you find a baby bird, since it is still best if you don’t handle a baby bird unless absolutely necessary.