Accidental poo. Need to consult doctor.

This condition is called encopresis and if your son was previously toilet trained and this behaviour you have been noticing recently it is termed 'secondary encopresis'. Though it may seem intentional due to his laziness sometimes, in fact child may be completely unaware that he's soiling. So never tease him or punish him. Child's self-esteem is important. There are few biological cause for the same, most commonest being constipation. Chronic constipation may result in painful bowel movements and child may postpone passing stools which may result in retention and incontinence which child is unaware of. Others are psychological causes like anxiety in the child, if there are stress factors like change in school, family conflicts, negative experiences with toilet training etc. This condition is completely treatable if the cause is found. So kindly do not panic. Support your child in whatever way possible. Good luck.

Consult a pediatrician for a detailed understanding of this problem and treatment.

Posting an useful link- read it for better understanding. https://childpsychologist.com.au/encopresis-soiling-in-school-aged-children/