Momma Swan & her 'swanling'? Okay, Google Now... 'The male swan (the cob) helps the female (pen) look after their babies, (cygnets, derived from the Latin word for swan, "cygnus") until they are a year old. The young don't spend more than one day in the nest once they hatch.'
They made a really bad movie of this really good Young Adult book. I liked the first book in the series the best but they were all fun to read. Post-Apocolyptic survival story about a town underground and cut off for 100 years from the rest of the world.