Three teenagers including a 13-year-old were charged with supplying drugs at an under-18s dance festival at Sydney Olympic Park on Saturday afternoon.

The trio, two aged 17 and one aged 13, were allegedly caught carrying MDMA capsules at Goodlife Lost City 2019, while a 16-year-old boy was issued a future court attendance notice for drug possession. A dozen other teens were issued cautions.

Crowds at the Secret Garden Music Festival. Credit:Anna Warr

Police also targeted drugs at the Ultra music festival in Parramatta on Sunday, which was put on the NSW government's new list of 14 "high risk" festivals that have either had serious drug-related illnesses or deaths or have been found to have a high risk of overdoses by police and health authorities, and will be subject to a tough new licensing scheme.

Police searched almost 400 people attending the festival, issuing 29 revellers with criminal infringement notices for possession of MDMA or cocaine and 13 cannabis cautions.