Luna has never seen anyone with a newborn baby before and she's never really thought about it either. When she sees Tonks with the baby she's almost envious at the tenderness between them, the way Tonks looks at the boy as if no-one else exists. Not even Luna.
Then Tonks hands her the child and Luna gets a bit dizzy at the thought of life in her arms, so fragile and special and entrusted.
'Say hello to mama,' Tonks tells the baby. He doesn't react, but Luna feels so very soft inside when looking into that tiny face. She smiles at no-one in particular when she realises that this is the first time "mama" is more than just a word they discussed calling her when this child was born.
Tonks leans back in the bed and closes her eyes and Luna kisses her forehead. Babies are exhausting, especially when they are born. Luna sits next to her as she dozes, still with the boy in her arms. She doesn't want to let go.
Two months later when baby Teddy burps and changes the colour of his eyes from blue to green, Luna is the only one who sees it. In that moment it is only her and Teddy and for the first time she knows what Tonks felt like that day when Luna didn't exist. Now she knows, truly, what unconditional means.