Visitors have made their choice of the most family friendly museum in Britain. It's not big, it's not housed in an imposing building, and it has no Egyptian mummies or dinosaur bones. The Herbert Art Gallery and Museum in Coventry is chock-a-block with a hotchpotch of items, from stuffed animals to displays on the city's Home Front and examples of woven silk. It doesn't sound promising for a fun afternoon out, yet families have picked it as the winner of the 2010 Guardian Family Friendly Museum Award. It proves it's not what you've got in your collection that counts, but what you do with it.

Six shortlisted museums were secretly visited by our undercover family judges. The families measured the museum against the Kids in Museums Manifesto – 20 ways to make a museum family friendly, compiled entirely from visitors' comments. After sneaking around and reporting back their findings, they picked the Herbert. The prize is 500 Quentin Blake illustrated Mammoth Activity Sheets, designed and donated by Foldedsheet.com.

Here's what some undercover family judges said:

Claire Jowett, 42: "We immediately felt welcome. When you go in there's a very open space – not like in other museums, where there's a desk in the middle. We ran straight into a workshop on designing an outfit. The vibe was so good; families were sharing and joking together. One of the ladies running it pointed out the fashion exhibition on the first floor. The children's Herbert logo leads you around the museum. The girls recognised it everywhere and then knew there was something for them, like an activity they could do."

Molly Jowett, nine: "We went to the front desk and I asked the lady if there was a family trail. There were different heights at the desk so I could ask my question very easily. She said, 'Think with me about what you'd like to see', so she wasn't telling me what to do, which was very good. I really loved the workshop. There were lots of materials, like lace and glitters and glue. I listened to audio stories on a headset. I heard actual people's memories, like this woman describing how she made dresses out of curtains during the war. One thing had a label saying 'Please touch'. Most of the times you are not allowed to touch anything in a museum!"

Ruby Jowett, five: "I was able to open the door to the bathroom myself. At other places the door is so heavy I have to ask an adult to help me. I dressed up as Lady Godiva in a nice coat, and I rode on the horse all around the room. I collected nice stickers and there were footprints on the floor to show which way to start. In every gallery there was a basket with pencils in it. Mama and Molly sat down and had a chat with other families. I was playing with another boy. When we left, the people from the front desk asked us to keep contact and they waved us goodbye."

Helen Rehman, 36, also visited with her husband, Mohammed, and their children, Alfie, four, and Izzy, 18 months. "I told Alfie we were secret museum inspectors. He was very proud, so told everyone about it. He shouted, 'Is this the secret museum?' when we arrived. His favourite part was 'Dressing up as a Cool Dude'. You get used to just being grateful for anything for your kids. But the manifesto focused our attention. Being undercover judges made us look in more detail at what they did."

The Herbert Art Gallery and Museum, Coventry, herbert.org, 024-7683 2386.

Do you want to be an undercover judge for the next Family Friendly Museum Award? Email award@kidsinmuseums.org.uk. To order a free copy of the Kids in Museums Manifesto, email manifesto@kidsinmuseums.org.uk. More about the award at kidsinmuseums.org.uk and guardian.co.uk/kidsinmuseums

© Guardian News & Media Limited 2010