Use 'cygnet' to describe swans only when they are young, similar to 'puppy' for dogs. The pond was full of beautiful cygnets this spring.
Pro Tip 2/3
Natural Setting
'Cygnet' often appears in nature-related discussions, especially regarding bird development. There is a special area of the lake where the cygnets are raised.
Pro Tip 3/3
Color Association
Cygnet' may imply whiteness as many associate young swans with white feathers, despite some being grey. The cygnets haven't turned white yet; they're still grey.