Girls are entering puberty earlier.
It is normal for girls with breast buds to want to wear those moulded soft cup bras and swimsuits, because they don’t want the outline of their developing breasts to be visible in public, because males of all ages will comment on it.
Covering up the shape is not about sexualisation anymore than women wearing T-shirt bras are trying to look more sexualised.
It’s not these girls’ faults or their parents that they are trying to disguise their nipples in a society that think the outline of a nipple is too sexual.