The Stephen Mulhern-hosted Britain's Got Talent spinoff featured burlesque dancer Scarlet stripping to The Jungle Book number 'The Bare Necessities'.
Director of content standards at Ofcom Tony Close said: "There is a clear line in terms of what it is acceptable to broadcast before the 9pm watershed.
"A striptease act broadcast at times when a significant number of children were likely to be watching clearly crossed this line."
He added: "The protection of children from potentially harmful content is a key area of concern for Ofcom, reflected in our ongoing work on the enforcement of the 9pm watershed
"We will continue to closely monitor compliance in this area and take appropriate action when needed."
Some of the images of Scarlet were pixelated, while the camera also cut away to show judges and audience reactions.
However, Ofcom said that the "frequency and close-up [nature]" of the naked shots meant that the pixelation had "limited effectiveness".
ITV had argued that it had shown similar burlesque-style acts in the past and was featuring not erotic acts but instead playing with "saucy humour".