In a new report published by the UK’s telecoms watchdog Ofcom, researchers found that only a third of young people aged 12 to 15 knew which search results on Google were adverts, while this figure was even lower — less than one in five — for children aged 8 to 11.
http://www.theverge.com/2015/11/20/9768350/google-ads-search-results-ofcom