Cecil was a kid Prompto was taking care of. Even from a distance, you could say that he's certainly not a biological father of that kid. Prompto found him alone in cold and decided to take good care of him... at least until his real parents are found.

"You see?! He's a mini me!" He declared like a proud father when the kid was waddling around the living room with his camera. "I feel like a real father..." He said with a theatrical expression.