Identifying what is, and what is not an advertisement is the first step in realizing that an advertisement is a marketing message. Children can distinguish television advertisements from programmes by about 5 years of age. Although previous researchers have investigated television advertising, little attention has been given to advertisements in other media, even though other media, especially the Internet, have become important channels of marketing to children. We showed children printed copies of invented web pages that included advertisements, half of which had price information, and asked the children to point to whatever they thought was an advertisement. In two experiments we tested a total of 401 children, aged 6, 8, 10 and 12 years of age, from the United Kingdom and Indonesia. Six-year-olds recognized a quarter of the advertisements, 8-year-olds recognized half the advertisements, and the 10- and 12-year-olds recognized about three-quarters. Only the 10- and 12-year-olds were more likely to identify an advertisement when it included a price. We contrast our findings with previous results about the identification of television advertising, and discuss why children were poorer at recognizing web page advertisements. The performance of the children has implications for theories about how children develop an understanding of advertising.