He is so cute! ⁄(⁄ ⁄·⁄ω⁄·⁄ ⁄)⁄ And I guess it’s because he’s a cherub and cherubs are physically portrayed as children! (Compared to his husband being an archangel if I remember correctly)
I think he's just short. It's important to note that they mentioned earlier in the story that his husband, the white haired angel is physically larger than the average angel.
he looks like a literal child