What do you have to do to get thrown out of a museum? Smear sticky fingers on the Persian tapestries? Scream so loud that other visitors can\'t thumb quietly through the browning albums of dried Azolla caroliniana? Do a cartwheel in front of a Caravaggio? Last week, two girls were asked to leave Salford Museum and Art Gallery. They were thrown out for being 13. The museum explained that their expulsion was \"for their own safety\". Like most self-respecting teenagers, they\'d gone out over half term without an adult. I don\'t for one minute believe the museum\'s action was prompted by concern for any child. If that were the case, why would they propel two girls into the streets of a busy town to wander across roads all on their own among total strangers? And sadly Salford isn\'t the only museum to discriminate against young people; many have similar bans. It\'s odd that Top Shop shares no such anxieties – my own teenager hangs out there and at vast, alienating shopping centres all the time. Libraries and leisure centres also welcome her and her friends without their mums in tow. So why is it particularly dangerous for teenagers to visit a museum unaccompanied? The real reason museums don\'t want them is not to protect children from danger, but to protect their precious objects and preserve their cathedral-like status. They are worried about how the teenagers will act within their highly cultured walls. Many museums argue, completely erroneously, that they don\'t have a choice; it\'s illegal to allow teenagers in by themselves. There is no such law. But there is an age limit. For a museum to allow a child to visit aged eight or under, it may possibly need to be Ofsted registered. But any older than that, it\'s up to the individual institution to set its own rules. It would be wrong to say museums shun all teenagers. They love them in school uniform, all besuited and trotting along behind a teacher. They are very keen to support \"out of the classroom learning\" as long as those having the lessons are accompanied by plenty of classroom assistants. They\'ll issue them with the modern-day equivalent of clipboards – hand-held electronic devices – and send them out on tightly controlled trails. Then they\'ll boast about how many young people have visited their museum each year, and how much they have learnt. Yet if these same teenagers turned up out of school hours, dressed in hoodies, T-shirts and trainers, they\'d get a very different reception. Many museums ban mobile phones at the door – sometimes the same museums that thrust gadgetry upon their school and youth-group visitors. On a recent visit to Tate Modern, even middle-aged me was told off by a gallery assistant for answering my mobile and asked to switch it off. Yet that same museum runs pioneering programmes with young people, involving some of the most hi-tech digital gadgetry available. That\'s not the only irony teenagers face when trying to access our artistic and cultural heritage. Over half of Britain\'s museums charge entry at the door. Many of these begin to charge full admission aged 12 and up, forcing teenagers to purchase an adult ticket. Yet if two 13-year-olds turned up on their own, they\'d be turfed out for not being grown up enough. There is another relationship museums could have with their teenage visitors. Museums are wonderfully safe places. As far as I know, no museum has suffered a spate of muggings or been the scene of a murder. It\'s unlikely that rival teenage gangs will wage turf wars under the Tintorettos or between the Stegosaurus and the Tyrannosaurus rex. It would be difficult to clandestinely shoot up by the glass cabinets of 19th-century French porcelain. There is no casual street violence in a museum, the thing we all fear our children will get caught up in. What wonderful places museums could be for teenagers in a sometimes threatening and troubled world. They could be havens from harm. They could, in fact, be places where teenagers could congregate, hang out and wander around unaccompanied \"for their own safety\".