Cybertronians are sparked into adult bodies, or grown from a the living metal of Cybertron itself; developing into their full bodies rather rapidly. he hadn't any reason to think that humans didn't work similarly. he supposes that he's seen children before but had simply assumed them to just be small-- like mini bots.

"I see." He narrows his eyes at the baby as it fusses in Deanna's arms. "Forgive my ignorance, I'm not excessively familiar with... humans. It must be rather new if it's so undeveloped." He barely manages to keep his disgust from leaking into this voice as the baby looks up at him, red faced and mouth dripping with drool.