Formal:
* Моя маленькая девочка (moya malen'kaya devotchka) - This is the most literal translation, meaning "my little girl."
* Моя дочка (moya dochka) - This means "my daughter" and can be used even for a baby girl.
Informal:
* Моя крошка (moya kroshka) - This means "my little one" and is a very affectionate term.
* Моя малышка (moya malyshka) - This means "my little one" and is another very affectionate term, often used for a baby girl.
* Моя любимая (moya lyubimaya) - This means "my beloved" and is a very loving term.
Other options:
* Моя принцесса (moya printsessa) - This means "my princess" and is a very sweet term.
* Моя солнышко (moya solnyshko) - This means "my sunshine" and is a very endearing term.
The best option for you will depend on the specific context and your relationship with the person you are talking to.