Small is only used for physical size (a big apartment / a small apartment).
Little can be used for:
▶️ Size (The cake is decorated with little flowers.)
▶️ Amount (Can I have a little milk for my coffee?)
▶️ Degree (I’m a little nervous.)
▶️ Size with an emotional expression.
This emotional expression can be:
o Adoration: Look at that cute little dog!
o Sympathy: That poor little girl has no mother or father.
o Dislike: I don’t want to go to her stupid little party.