A “loophole” that allows sports coaches to legally have sex with 16 and 17 year olds in their care must be closed by the government, the NSPCC has said.
It is already illegal for certain professionals, such as teachers and social workers, to do the same.
The NSPCC said it was concerned that the role of sports coach, and other youth workers, fell outside the legal definition of a “position of trust”.
The government said it was committed to ensuring sports participation was safe.
The charity’s chief executive, Peter Wanless, told the BBC’s Victoria Derbyshire programme that the loophole was “remarkable… given the significant amount of responsibility, influence and authority that an individual in [the role of sports coach] can hold in a young person’s life”.
He said it was vital to “bolster protection for teenagers at risk of grooming once they pass the age of consent”.
This call for change comes after the charity said in December that more than 1,700 calls had been made to the hotline it set up with the Football Association in the wake of claims of sexual abuse in the sport.
Mr Wanless said alerting the government to the loophole was “not about demonising certain jobs, but about protecting young people from a small minority of adults only too happy to take advantage of their standing in society to groom and abuse vulnerable children”.
The charity also wants the government to tighten the rules around background checks, which tell a club if a coach has a criminal record or is banned from working with children.
In 2012, then-Home Secretary Theresa May relaxed the rules, meaning only an employee or volunteer working unsupervised with under-18s on a regular basis could face a full check.
The NSPCC believes that went too far, and that people who are barred from working with children are able to take up assistant or support roles in children’s clubs “completely undetected”.
The pressure group Mandate Now, which campaigns for tighter rules around child protection, said the changes, if implemented, would not go far enough.
It wants the UK to follow countries like the US, Australia and Canada, where there is a legal responsibility for people working in regulated activities like sports clubs to report suspected abuse to the authorities.
“The NSPCC proposals are one small step for child protection, but not a giant leap for it in sport or any other regulated activity,” said the group’s Tom Perry.
In a statement, the Department of Culture, Media and Sport said the government was “completely committed to doing all it can to ensure people can participate in sport in safe and secure environments”.
It added: “In November we wrote to sports governing bodies to look at their own safeguarding practices, to make sure they are as robust as possible, and that work is ongoing.”
Watch the Victoria Derbyshire programme on weekdays between 09:00 and 11:00 on BBC Two and the BBC News channel.