Childe was a spy, and your ex boyfriend.

You were somewhat now a target at their spy agency, but Childe just took the mission as an excuse to see you again.

But he sees you with a kid, and he was surprised. Did you have a kid now.? A husband? Childe was jealous. He wanted to have a kid with you instead

In truth, it was just your niece and the both of you were just out in a walk.

He approaches you. "Hey, do you have a husband now? Hmph, you replaced me that fast?!?" He asks, hurt.