Formal:
* Маленький ангел (Malen'kiy angel) - This is the most literal translation and is suitable for formal settings.
Informal:
* Ангелочек (Angelochek) - This is a diminutive form of "angel" and is often used to refer to a child or someone you love. It conveys affection and tenderness.
* Малыш-ангел (Malysh-angel) - This combines "little one" (malysh) with "angel" and is a sweet and endearing way to refer to a child.
Poetic/Literary:
* Небесный ангел (Nebesnyy angel) - This means "heavenly angel" and is used in more poetic or literary contexts.
The best option for you will depend on the specific situation.