The aunt of a 12-year-old girl has shared screenshots online of the adverts her niece was served up on Instagram during the course of a day.
Every single one was based around fashion or beauty.
The girl, who is just about to turn 13 - the minimum age for Instagram - has recently joined the social network.
Instagram said its ads are based on a number of factors, including who the account holder follows, and other websites they visit.
The girl's aunt, author Tamsin Winter, told the BBC she was "saddened" by the ads, and claims they do not reflect the interests of her niece, who she described as sporty and academic.
Ms Winter had asked her for the screenshots, as she was preparing to give a talk about body image and confidence.
"I expected a bit of a range - there was no range whatsoever, every single ad was about beauty or fashion," she told the BBC.
"Even one which was promoting something healthy, like gym wear - the model isn't doing anything healthy, she's fiddling with her hair."
Instagram's ad policy states that health, fitness and weight loss ads must be targeted at those aged over 18.
"There are lots of things you think about with your kids on social media, but advertising isn't really one of them," said Ms Winter.
"I told her, 'I hope you know it's not the case that beauty is all that matters'. She said a lot of her friends are on diets and think they need to look a certain way."
Analyst Jack Kent, from IHS Markit, said social media advertising tends to be based on anonymised data reflecting the account holder's interests online, alongside other information, such as which device they are using and their location.
"The placement of specific ads on a user's newsfeed will be based on that profile, and of course an advertiser's willingness to pay for targeting that type of user," he said.
If you are an Instagram user and you would like to see which ad categories the platform has assigned to you, go to the settings menu in the app, then follow this path: Security / Access Data / Ads / Ads Interest.