When he was small my son loved to be in the garden. At first, stones and mud and sand fascinated him and later flowers and worms and insects. And as he grew, in those precious days before he started school, I loved the way Richard made sense of his world: discovering and exploring before asking. So refreshingly unlike me.

Then one night it all changed.

We had just fitted a house alarm and sometime during the night it went off. We thought it was just teething problems but I went straight to look in on Richard anyway.

His bed was empty. He was gone.

I ran downstairs and there, standing beside an open front door, was a very frightened little boy. I hadn’t realized he’d grown so much. He could reach the doorknob if he stood on a stool. So the alarm had worked after all – not keeping intruders out, but keeping Richard in.

He was too young to explain much but he told me had done it before. He would wake in the night, wander round the garden and into the street and then return to bed. He wanted to know what it was like to be outside in the dark. I’m not sure how many times it had happened but I knew I’d failed to keep him safe and I had to tell him – You can’t do that again.

That night I had to make Richard’s world a little smaller.