Obviously, it is normal in toddlers and younger children. However, you should be concerned if it carries on after the age of four. By then, your child should be able to use the toilet regularly. There are two main causes for soiling. A child can suffer from both of them.
Severe constipation causes the bowel to be blocked with hard faeces.
The child finds it painful to pass these, and so becomes more constipated. Liquid faeces then leak around the blockage, staining clothes. Not learning a regular toilet routine is a common cause. The child may be reluctant to use the toilet. This may sometimes be part of a general pattern of behaviour, where a child refuses to do what you want them to.