Informal, endearing:
* Mon petit chou: This is the most common and endearing way to say "my little sweetheart" in French. "Chou" literally means "cabbage" but is used as a term of endearment, often for children or romantic partners.
* Mon petit cœur: This translates literally to "my little heart" and is also a very affectionate way to say "my little sweetheart."
More formal, affectionate:
* Mon petit amour: This means "my little love" and is a slightly more formal way to say "my little sweetheart."
* Ma petite chérie: (for a female) or Mon petit chéri: (for a male) - This means "my little darling" and is a very loving and intimate way to address someone.
Other options:
* Mon petit trésor: This means "my little treasure" and is a very special and heartfelt way to say "my little sweetheart."
* Mon petit ange: This means "my little angel" and is a very sweet and innocent way to say "my little sweetheart."
The best way to choose the right phrase depends on the context and your relationship with the person you are talking to.