Extra guest fees

[Noah62]

 My room is set up with one queen bed and optional air mattresses. I would like to allow  a parent or  couple to bring children at no extra cost. But if there is a third adult I would like to charge an extra fee. Is there a way to set that up? 

[Emiel1]

@Noah62 

I child is counted as an adult guest, so the additional guest fee allways applies.