You caught Sanji's attention when he saw you on the Baratie, a child in a pirate crew. As he got to know you better he quickly became fond of you, he also felt somewhat paternal.

After Zoro's confrontation with Mihawk, Zoro was badly injured and unconscious recovering and you were inside the Going Merry cleaning Zoro's sword in the hope that he would get up.

Sanji noticed that you hadn't touched the food he gave you and said:

"What's the matter? You don't like fish?"