More than 11 million people are expected to be subject to checks
Parents who regularly drive children for sports or social clubs will have to be vetted or face fines of up to £5,000 under new rules.
Along with parents who host foreign exchange students, they will fall under the scope of the Vetting and Barring Scheme, the Home Office has confirmed.
The measures to stop paedophiles are being introduced from next month in England, Wales and Northern Ireland.
Critics have branded them "insulting" and say they could deter volunteers.
A separate but aligned scheme is being set up in Scotland, to be introduced next year.
Also, anyone barred in any part of the UK will be barred from working with children and vulnerable adults anywhere else.
Informal arrangements between parents will not be covered, but anyone taking part in activities involving "frequent" or "intensive" contact with children or vulnerable adults three times in a month, every month, or once overnight, must register, it has emerged.
The government's Vetting and Barring Scheme is a child of moral panic
All 300,000 school governors, as well as every doctor, nurse, teacher, dentist and prison officer will also have to sign up.
It is thought that 11.3 million people in England, Wales and Northern Ireland - close to one in four of all adults - may register with the Home Office's Independent Safeguarding Authority [ISA].
According to BBC home affairs editor Mark Easton it is thought out of that 11.3 million, "something will come up", such as a conviction, for about one million.
"Of those million, they reckon 40,000 will be told they are unsuitable to work in those regulated areas," he said.
After November 2010 failure to register could lead to criminal prosecution and fine. The clubs themselves also face a £5,000 penalty for using non-vetted volunteers.
Children's minister Delyth Morgan said: "It is about ensuring that people in a position of trust that work frequently and intensively with children are safe to do so.
"Ultimately safeguarding children is the government's priority."
Shadow home secretary Chris Grayling said: "This new regime has the potential to be a real disaster for activities involving young people.
"We are going to drive away volunteers, we'll see clubs and activities close down and we'll end up with more bored young people on our streets."
Children's Minister Delyth Morgan: "Safeguarding children is number one priority"
Liberal Democrat home affairs spokesman Chris Huhne said the government was "in danger of creating a world in which we think every adult who approaches children means to do them harm".
But John O'Brien, programme director of the Vetting and Barring Scheme, said it would be a "once-only, simple step". He denied it was a "presumption of guilt".
He told the BBC's Today programme: "We want to make sure we have got appropriate safeguards in place so that people with backgrounds we don't want to work with children and vulnerable adults are not entering the workplace."
Bob Reitemeier, chief executive of the Children's Society, said the new safeguards were the result of many years of research into abuse.
"What we have to understand is there's a great amount of learning that has been taking place over the years in looking at how people are abused and we have to apply that learning."
The scheme was recommended by the Bichard report into the Soham murders of Holly Wells and Jessica Chapman by college caretaker Ian Huntley.
Huntley had been given the job despite previous allegations of sex with under-age girls, which were not passed on.
Two hundred case workers at the ISA's Darlington base will collect information from police, professional bodies and employers, before ruling who is barred.
The rules aim to stop those like Soham killer Ian Huntley accessing children
Even those like Huntley, without a criminal record, could be barred if officials are convinced by other "soft intelligence" against them.
Estimates suggest the number of people facing a ban will double to 40,000 once the scheme is up and running.
Those registered will face continuing scrutiny, with existing registrations reconsidered if new evidence is disclosed.
However, Soham report author Sir Michael Bichard suggested the scheme could be revised.
He told the Independent newspaper last month: "If you visit one school in January, and then don't visit that school again, but visit another school in February and another in March, is that frequent or intensive?"
He was speaking after a number of authors, including Philip Pullman and Michael Morpurgo, complained the requirement was "insulting" and pledged to quit school visits.
Mr Pullman described the scheme as "rather dispiriting and sinister".
"It's so ludicrous that it's almost funny," he said.
Registration will cost £64 in England and Wales, but unpaid volunteers will be exempt from the charge.
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