I figure it's possible they met when they were kids.
Ambroise is a few years older than Armand, but he's never looked his age. They met at a park, Ambroise was by himself, and Armand (thinking he was much younger) "took care" of him. Ambroise bought him an ice cream, then kissed him on the cheek when he had to go home.
Ah, young love. And lazy "coloring".