The channel has been accused of peddling obscenity over its Sex Education Show, aired just before prime time.
Among the scenes was a discussion about safe sex in which a doctor uses vegetables to teach a group of young men how to put on a condom correctly.
In another segment, a doctor examines a man's genitals and explains how it functions during a sex education lesson.
The show saw school pupils asked to discuss pornography and inspect graphic images of genitalia.
Teenagers were seen describing depraved sex acts they had seen on the internet and relevant footage was screened before the parent participants, one of whom looked like she would throw up on the show itself
Other parts of the hour-long show, aired on Tuesday and the first in a series, saw a men's football team drop their shorts before repairing to the lavatories where they were said to have measured the size of their sexual organs.
A group of boys were shown close-up images of penises and asked which they thought was the average size.
A male model's genitals were also shown in close up as a female doctor described in depth the anatomy of the penis.
There were also intimate waxings and a group of schoolgirls looking at pictures of different size breasts.
Presenter Anna Richardson was seen attending a Tantric sex tuition session before she tried it out on her partner.
The children who took part in the programme, who attend an unnamed state school, were aged between 15 and 16. Their parents had given full consent for them to take part.
One viewer contacting a TV message board said Channel 4 was 'reaching new lows' and added: 'This was nothing short of legalised porn.'
John Beyer, director of the TV pressure group Mediawatch UK said he had received a number of complaints about the programme. He claimed that in his opinion what had been broadcast was 'obscene'.
Beyer said: 'People are absolutely appalled and astonished something like that was put on by Channel 4 at 8pm.
'I find it extraordinary that they could put this on at that time.
'It is so early and it seems to me that Ofcom has got to answer how this is not in breach of the statutory requirement to protect under-18s.'
Shocked viewers said Channel 4 was guilty of broadcasting indecency into family homes.
They claimed it had broken the rules aimed at protecting youngsters from inappropriate material and said they were baffled it showed the programme so early in the evening.
"Shouldn't this programme have been shown post-watershed?" said one viewer during an online discussion about the show.
"Does everything have to be done on TV these days?"
Others accused the broadcaster of once again employing tawdry tactics to gain viewers.
Conservative MP David Davies lashed out, 'This doesn't so much seem a sex education programme as an excuse to shock people with controversy in order to boost ratings.'
He added: 'Some people derive sexual satisfaction in the most bizarre manner.
'But do we really need to have these things graphically discussed by schoolchildren at 8pm in the evening when we are having our tea?'
The show had a peak audience of 3.3million, which the broadcaster heralded as a success.
The six-part series is also due to cover abortion, homosexuality and pregnancy in the coming weeks.
Another said: "Channel 4, we're not shocked any more. Do stop these infantile and puerile programmes on sex and start making decent documentaries. Put it away please, nobody's impressed."
The series is accompanied by a website, entitled Sexperience, which young children can easily access.
It tackles a series of sexually explicit questions, including "Have you ever had a problem having an orgasm?", "How do you and your partner get in the mood for sex", and "Do you reckon having phone sex and text sex counts as cheating?"
The media regulator Ofcom confirmed that it would investigate complaints from shocked parents.
But Channel 4 defended the show, saying it was meant to provoke discussion amongst families and said the scene of nudity had clearly been signposted before the start.
"Whilst we did receive a small number of complaints we also received some very positive feedback," a spokeswoman said.
"The series is aimed at families and we hope it will act as a starting point for a family discussion about the important issues raised.
"The show was preceded with warnings about content and scenes featuring nudity were flagged prior to each part of the hour-long show."
A Channel 4 source added the number of complaints had been relatively small for such a potentially controversial show.
"We haven't had that many complaints really - not of the amount that you would think was quite worrying and we got quite a lot of appreciative calls," the source said.