'Little one' as in baobao or baobei?

that's honestly a good question, in the chapter it was "小傢伙" but due to the next chapters coming its mostly more Baobei.

What is the difference?

Baobao = Often used by parents to refer to their young children, similar to calling a child "sweetie" or "kiddo". 

Baobei: Used to refer to lovers, young children, or anything one holds dear.

Good to know. Thanks sm