The boy is dressed like a girl cuz Josh (the omega dad) really likes Chase’s face. (the alpha father) In their story, Josh first falls in love with Chase when he shows up on TV as a child actor, cross dressing as a girl in a chocolate commercial. Their second child, Cecil, resembles Chase more while Pete looks more like Josh. The second child also knows that Josh is fond of Chase’s face and about the chocolate commercial (or Josh’s natural tendency to like when Cecil dresses feminine due to his nostalgia and love for Chase) and so Cecil dresses as a girl to get more love and attention from Josh!
For Josh too, and Josh started dressing him in cute clothes (Chase sometime wears female clothes for Josh, by the way lol), but Cecil hated it. Why he started to do it willingly has to do with Spence. That extra wasn't adapted to manhwa. Actually half of the existing side stories are not adapted to manhwa.
So does this mean Spence is going to end up with one of Josh's boys?? They're both fighting over him or am I wrong?? Are they getting a story too?? Is that why the little boy dress as a girl or???