Maybe they were born with moustaches or got them as babies (I don't see as from birth meaning they had ti be born with it, but that it happens very early. Gestation is short for growing long hair like Raditz). Only as absurd as being a baby with Goku's hair or having a tail.
Daima or Super contradicts it tho. It shows child Raditz and his hakr isn't thta long. Actually, child zvegeta and xhild golu should hav é heads dwarfed by their hair.
Speaking of plot, did thejr GT hair ever affect the plot? Like Vegeta training harder because of Bulla making fun of hus moustache? Or 17 not recognising him? Or using a razor t shsve his eyebrows ti scare Baby into thinking he'd attained SSJ3? Letting Baby control him because Baby told him he knows where to buy a value pack of razors? (even tho his wife nad fstherinlsw are maybe the richest on Earth)