The regulator received two complaints after the ad, for the online clothing retailer CharGrilled, appeared in the April issue of Viz magazine.
It showed a young girl wearing a T-shirt and holding a glass of wine and a cigarette, while the text of the ad read "BE A COOL KID - Wear a CharGrilled T-Shirt".
The complainants challenged whether the ad breached regulations because it featured a child who appeared to be drinking alcohol and smoking and because it suggested that doing these things would enhance a person’s popularity.
In its response CharGrilled said it did not feel the ad enhanced the popularity of drinking or smoking but it accepted that the girl appeared to be under the age of 25, which breached the ASA’s rules, and withdrew the ad.
The company said it had taken the image from a stock photo library and had not chosen the specific model that appeared in the ad.
Dennis Publishing, the publishers of Viz magazine, said it had not received complaints from its readers but accepted that the ad should not have run.
The publisher pledged to review its advertising practices so that the same issue did not happen again.
In its ruling the ASA said the girl in the ad, "appeared to be around nine or 10 years old" in breach of its regulations which state that people shown drinking or playing a significant role in ads featuring alcohol must not be, or seem to be, under 25-years-old.
ASA rules also state that ads featuring children must not contain material that was likely to result in their physical, mental or moral harm or encourage children to copy practices that were unsafe for them.
"We considered that both smoking and drinking alcohol were practices that were likely to result in harm to children," the ASA said in its ruling, adding that the ad’s text appeared to condone underage drinking and smoking.
The ASA found that the ad breached its codes on responsible advertising, harm and offence, children and alcohol.
The regulator welcomed CharGrilled's assurance that the ad had been withdrawn and told the retailer that future ads must not feature children appearing to smoke or drink.