It is a common phrase used to ask someone what's going on, especially in a friendly and informal way.
The word "bambino" is an Italian word for "baby" but is often used in Spanish as a term of endearment for someone, typically a young man.
Here are some examples of how the phrase can be used:
* "Qué pasó mi bambino? ¿Cómo estás?" (What happened, my baby? How are you?)
* "Qué pasó mi bambino? ¿Qué te trae por aquí?" (What happened, my baby? What brings you here?)
* "Qué pasó mi bambino? Te estaba buscando." (What happened, my baby? I was looking for you.)