There's no set age when you know it will be safe for your child to go out without you. Obviously, toddlers and young children won't be able to stay safe without you watching over them, and even older children have different levels of maturity. Although some 11 year olds will be quite capable of going to the park or the shops on their own, others might not be ready to do this safely.
Your decision may also depend on where your child is planning to go. For example, going to the playground round the corner is very different to catching a bus to the local shops.
This guide will help you to decide when your child is old enough to be out on their own, and how to teach them to keep safe while they're away.