Many would have predicted Jacqueline Wilson's children's books would, despite their fluorescent covers, prove either too grim or too worthy for the best-seller lists.

Although dealing, as they do, with the effects of divorce, affairs, death and parents who are either absent or in some way ineffectual, this ignores what Wilson instinctively recognised - that snogging and sex are a big part, but not the whole story, when it comes to young people's inner lives.

Since writing her first novel for the age group in 1973, Wilson has published more than 50 children's books, selling 15 million copies, getting four titles in the BBC Big Read's top 100 and recently overtaking Catherine Cookson as the most-borrowed library author in the UK.

She is the sort of author children will save up for, queue round the block for and get uncharacteristically possessive about when TV adaptations fail to match her straight-up, unsentimental approach or the colours of her characters' hair.

Undeterred, in 2003 popular children's company Polka Theatre decided to put Wilson's Double Act, about two identical but very different twins, on the stage.

Adapted and directed by Vicky Ireland, it was not only a success with its audience, reaching more than 130,000 people across the country, it also received a resounding thumbs-up from the author.

"It's the most inventive, magical, enriching company," she gushed. "They don't think they can relax standards because this is a theatre for children - they strive extra hard because it's for children and only the very best will do. Polka is the best. For many of the children it will be their first experience of the theatre - and it's one they'll never forget."

Now the same team have turned their hands to the slightly trickier subject matter of Bad Girls, Wilson's eighth book and one of her most popular.

Newly decked out in some "cool choreography" and "magical lighting", this is the story of Mandy, a bright ten-year-old who always gets good marks at school but is embarrassed by over-protective, out-of-touch parents.

Cast out by her so-called school friends, Mandy is delighted when a cheerful, trendy 14-year-old named Tanya moves in with her foster parent across the road and, because Mandy reminds Tanya of her much-loved kid sister, now in care, she is also eager to make friends.

Tanya's unhappy life has made her turn to petty crime, however, and before long Mandy finds herself in deep waters.

With Susan Harrison and Luanna Priestman receiving favourable reviews in the lead roles, the main reservation among critics seems to be whether a two-hour play is too long for a target audience of 8-12 year olds. Maybe they should take a lead out of Wilson's book and stop with the condescension?

Starts 7pm, with 2pm mat Sat, Tickets £8-£14, Tel 01273 647100