Paltrow's Goop.com site sells swimwear designed by Melissa Odabash, and shows pictures of a little girl wearing one of the two-piece creations, as well as beach cover-ups.
The outfits, which are described as "great for girls who want to look grown up", have sparked outrage among campaigners who claim the images sexualise children, reports dailystar.co.uk.
"We remain very opposed to the sexualisation of children and of childhood. The dangers have been discussed at length, so it is a great pity that such trends continue and that they carry celebrity endorsement," Claude Knight of Kidscape, a foundation set up to prevent child abuse, told the Daily Mail newspaper.
Photos: Ajay Devgn, Parineeti, Tabu at 'Golmaal Again' trailer launch
Photos: 'Dangal' girls Sanya Malhotra, Fatima Sana Shaikh's dinner outing
Photos: Kareena Kapoor Khan's grand birthday bash
Photos: Salman Khan, Daisy Shah spotted at the Mumbai airport
Photos: Rakhi Sawant to play Honeypreet in Ram Rahim biopic