Four leading web providers are to offer customers the option to block adult content at the point of subscription, the BBC understands. BT, Sky, Talk Talk and Virgin will offer the protection for smart phones, laptops and PCs. It comes as David Cameron is set to meet industry representatives amid concern over sexualisation of children. The prime minister will also launch Parentport - a website to help parents complain about inappropriate content. And he will back a ban on billboards displaying risque images near schools. The new measures, aimed at helping parents protect their children from internet porn and other explicit sites, follow a report earlier this year by the Mothers\' Union charity. Top videos Its head, Reg Bailey, warned that childhood was being wrecked by the \"commercialisation and sexualisation\" of children on TV, amongst advertisers and on the web. Mr Cameron is due to meet Mr Bailey at the Downing Street summit later, at which he will also urge companies not to use children to market goods to other children. The changes proposed in Mr Bailey\'s review include restricting steamy pop videos to older teenagers and later television slots and covering up magazines on shelves that feature sexualised images. In a letter to Mr Bailey in June, the prime minister wrote: \"As you say, we should not to try and wrap children up in cotton wool or simply throw our hands up and accept the world as it is. \"Instead, we should look to put \'the brakes on an unthinking drift towards ever greater commercialisation and sexualisation\'.\" Mr Cameron added that he welcomed recommendations to make it easier for parents to block \"adult and age-restricted material\" across all media. He also said he supported banning the use of children to market goods to other children. Telecoms watchdog Ofcom said the launch of Parentport would make it easier for parents to complain about material they had seen across the media, communications and in retail. It said the website had a \"have your say\" section where parents could give informal feedback and comments and also offered advice on keeping children safe online. Chief executive Ed Richards, said: \"Seven UK media regulators have come together to develop a single website, with a single aim - to help protect children from inappropriate material. \"Each regulator shares this common purpose and is committed to helping parents make their views and concerns known.\"