The first episode of the series, fronted by Anna Richardson, was shown on Tuesday night and attracted an average audience of 2.6m between 8pm and 9pm, well above Channel 4's slot average.
The show featured teenagers discussing sex acts they had seen on the internet, before parents were shown the footage of what their children watched.
Another segment of the show featured a group of boys looking at close-up pictures of penises and being asked which they thought was the average size.
Richardson was seen attending a tantric sex tuition session, while a doctor used vegetables to teach a group of young men how to put on a condom correctly.
Some viewers claimed that Channel 4 was guilty of broadcasting indecency into family homes and couldn't understand why it was shown before the 9pm watershed.
Others accused the broadcaster of showing sexually explicit material to gain viewers.
The six-part series is also due to cover pregnancy, abortion and homosexuality over the coming weeks.
Channel 4 defended the show saying that it offered viewers important advice aimed at reducing teenage pregnancies and sexually transmitted diseases.
The broadcaster said that it had received a small number of complaints but that the programme was aimed at families as a starting point for discussion about the issues raised.