Especially since has to take over as father (literally). They're just like ducks, how they stay close to each other like mother duck and her ducklings. Even Clemont protects her. I think something happened to both parents leaving poor Clemont alone with little Bonnie.
Of course they always do. Their parents are maybe out in a different region working as inventors or scientists to the point where they can't care of their own children. I hope we get a cute flashback of Clemont with his mother or father or both.
Here's how I think they might turn out.
Father- Young Clemont walks into a room where he sees his father working on an invention. Clemont decides to get a closer look at it. So he walks closer and gets his hair ruffled by his father.
Mother- His mother is pregnant with Bonnie and young Clemont walks over to her and hugs her stomach and says "Hi baby". Then his mother asks him "Are you excited to be a big brother?" and he'll squeal out "Yes!".
Mother and Father- Basically when Bonnie was born. Young Clemont watches his mother come home from the hospital with baby Bonnie, he joyfully runs over to her asks "Mommy may I hold my baby sister?!" then she'll say "Clemont let your dad help you". Clemont is soon sitting on the couch next to his mother and father, they help him hold Bonnie properly.