New laws to clamp down on anti-social behaviour will "promote intolerance of youth" and damage the relationship between young people and the police, the children's commissioner and leading organisations representing young people warn today.

In a letter to the Observer Dr Maggie Atkinson, children's commissioner f in the Anti-Social Behaviour, Crime and Policing Bill going through parliament.

They say the proposed clampdown on unruly behaviour will "punish children over the age of 10 simply for being children" by widening the definition of antisocial behaviour and reducing the burden of proof so sharply that the effect could be to "outlaw everyday activities" such as skateboarding or ball games. The Home Office argues that the measures will deliver speedier and more effective curbs on unruly activity.

Under the proposals antisocial behaviour orders (asbos) will be replaced by new Injunctions to Prevent Nuisance and Annoyance (ipnas).Currently, to be given an asbo a person must have behaved in a way that "caused or was likely to cause harassment, alarm or distress". But under the new law, a person would have to have behaved only in a way that is "capable of causing nuisance or annoyance" to get an injunction.

For a court to grant an asbo, it must be satisfied "beyond reasonable doubt" that a person has behaved antisocially and conclude that an asbo is necessary to protect others from further antisocial acts.

But to grant one of the new injunctions, the court would have to believe only that "on the balance of probabilities" a person had behaved antisocially and to conclude that it is "just and convenient" to grant an injunction to stop their antisocial behaviour.

Opponents say that under the new law, if the police or local council believe that "on the balance of probabilities" a weekly basketball game is capable of annoying residents and that an injunction would be a convenient way to stop the game, they could ask the court to issue an injunction against the players. This would restrict where the players could go and what they could do. If the players were over 14 and they flouted the injunction, they could be imprisoned for up to three months.

Signatories to the letter, who also include the chief executive of the National Children's Bureau, Dr Hilary Emery, say that the measures amount to an overreaction which is particularly unfortunate at a time when youth services are being cut across the country.

They write: "We acknowledge that antisocial behaviour can blight the lives of individuals and communities, but this bill is not the answer. It promotes intolerance of youth, is a blow for civil liberties and will damage children's relationship with the police. Children learn the importance of right and wrong from their parents, teachers and communities. We do not need to create more laws to do it."

Last week the human rights joint committee of both houses of parliament also called on government to amend the Bill "to make the test for anti-social behaviour more precise".

Penelope Gibbs, chair of the Standing Committee for Youth Justice, said:"It's hard to believe that the government is planning to outlaw teenagers just for being annoying – unopposed by Labour. Many teenagers already feel they are pariahs in their communities. What are teenagers supposed to do? Youth services have been cut, they are told not to spend too much time indoors playing computer games. Yet this law means they may be afraid to skateboard on the street or just hang out with their friends."