can a sleep walker open a chain lock?

There is no known cause for sleepwalking but most children will outgrown it.

In the mean time, you can make sure any windows and doors are locked. Locks can be attached outside their door and high up so no one but an adult can reach.

When you find your child sleepwalking, gently guide them back to bed and try not to wake them.

It sometimes helps to establish a consistant bedtime ritual that will reinforce that bedtime is for sleeping. This can include readings a story, a bath a tuck in and hugs.