The mother of a schoolgirl was left "gobsmacked" that police left a bag of speed in her daughter's schoolbag.
Kia found the drugs in her bag when she got home
Kia Butterfield, 10, discovered the bag of amphetamines at home after an anti-drugs day organised by her school.
Her mother Amanda said: "You don't expect your daughter to go to school and come home with drugs in her bag."
Lincolnshire Police are investigating how the mix-up happened but said an officer neglected to collect the drugs after a sniffer dog demonstration.
Police collected the drug and apologised to the family on Wednesday, she said.
The drug awareness session was held at Butlins near Skegness as part of the Frank's Party drug education programme.
The family from Wainfleet told BBC News they are shocked at what happened and want to make sure security arrangements are tightened so the mistake does not happen again.
Mrs Butterfield, 33, said: "I am pleased Kia is sensible and did the right thing by handing the drugs over to her father - and the police did the job to get the message across.
"But I am very annoyed it did happen."
She added her two younger children aged one and three were running around the house at the time and might have thought the bag of speed was sweets.
Ch Supt Dave Wheeler for Lincolnshire police said: "When the packages were being hidden two packages were inadvertently placed in the girls bag and when the dog found the drugs only one package was retrieved.
"It was a training exercise for the dog and education for the children but what happened shouldn't have happened."
He said a review is under way but steps have already been taken to make sure it doesn't happen again.
Peter Beveridge, head of Wainfleet Magdalen Primary School, said 35 pupils were at the event and added that the incident "should not detract from the drugs awareness message".