Headteacher Andrea Batley has reminded them the drug is illegal and the families of pupils aged between four and seven whose clothes and book bags smell of it will be reported to police and social services.
Her reprimand comes in the October 7 newsletter for parents and carers at Longshaw Community Infant School on Crosby Road in Highercroft, Blackburn.
Mrs Batley has received several reports from staff and fears for the effect of second-hand cannabis smoke on her pupils’ health if parents or their friends take the drug around the children.
Cllr Maureen Bateson, Blackburn with Darwen Council’s schools boss, said she was ‘concerned’ and backed the school reporting families to the police and social services.
Borough Conservative group leader Cllr John Slater said it was ‘disappointing’ an infant school head had to give the warning and supported any further action taken.
The 220-pupil council-run school is rated ‘Good’ by Ofsted.
Mrs Batley’s newsletter says: “Please can I draw attention to the fact that cannabis remains an illegal drug in the UK and therefore children’s clothing and book bags should not smell of this substance.
“We have had a growing number of reports from staff regarding this issue and therefore we are in the process of developing a policy which will note when children’s clothing or possessions smell of cannabis and the school’s legal duty to inform other agencies.”
Cllr Bateson said: “I am not surprised to find that we have pupils who have been in contact with cannabis within families.
“But I am concerned about this and I am concerned about its impact on the health of the children and on their mental health.
“I am particularly worried the pupils involved are so young and I would think that the younger the child the more serious the effect.
“I am also concerned about the danger to babies and children not yet of school age in these families.
“As far as I am aware this is an isolated incident. Where appropriate I would support the parents or carers being reported to the police and social services.
Cllr Slater said: “This is disappointing. Inhaling cannabis fumes could have a serious effect on the children’s health and particularly their mental health.
"I would fully support the families involved being reported to the police and social services.”
Mrs Batley said: said: “I wanted to inform all our parents we will consistently take appropriate action when we suspect children are being subjected to second-hand smoke inhalation, especially relating to illegal substances.
“Cannabis use everywhere is becoming more prevalent.
"However we will be reporting any incidents to the police and children’s social care where necessary to protect our children from the harmful impacts of second-hand smoke and exposure to illegal substances.
“Unfortunately this is not something unique to this school.
"We know other schools across the country have taken similar approaches.
“This is only happening in a small minority of homes.
"However it is completely unacceptable and not fair on the children to come to school with their book bag and clothing smelling of cannabis.
"A number of parents have contacted me to say that they are glad the issue is being addressed. ”
A police spokesman said: “Where concerns are raised we will liaise with the school and where appropriate we will take proportionate action .”
Local Blackburn South-East ward’s councillor Andy Kay said: “I am clearly concerned about this and I hope the school will be talking to the families involved.”