The thing is, as a man who very much appreciates women and feminine beauty, I have never given a single solitary thought to the word "panties" being either infantile of sexualized. Panties are panties whether they're on a beautiful sexy woman, a two-ton-tessie, or a 4 year old. It is just what women's underwear is called. I am willing to bet that somewhere upwards of 80-90% of men would say the exact same thing.
Now to be honest regarding the aforementioned two-ton-tessie, I might be inclined to jokingly refer to her panties as "bloomers" or some other disparaging term indicating her size. But they're still panties.