Clarification on DS, DD......?

[Brightday]

Everyone is talking about DS or DD, etc...
Obviously, I'm not an up-to-date mum but what does it mean?
DS I could understand and Daughter and Son, but DD?

this should help

D is generally considered to stand for Darling or Dear, but conveniently enough can also stand for Dratted when you've had a particularly trying day...