The boys were found inside the Sainsbury's store at 2am on Tuesday.
Lib Dems: Drugs Approach Must Change
Nearly 1,000 people have been imprisoned for possession of drugs in the last five years rather than sent for treatment or education, Scottish Government figures show.
An average of 200 people a year are imprisoned for possession but just 55 a year are given drug treatment and testing orders, figures obtained by the Liberal Democrats reveal.
The Lib Dems want an end to the use of imprisonment for people addicted to drugs, calling for it to be treated as a health issue instead.
Drug dealers would still face criminal sanctions and people failing to abide by treatment or education plans would be subject to additional penalties.
Mr Rennie will be campaigning in Glasgow on Sunday, where 189 people died as a result of drug misuse in 2014.
He said: "Drugs blight communities right across Scotland but the way that we tackle addiction is broken.
"Here in Glasgow, 189 people died as a result of drug misuse in 2014. 189 families who lost a son or daughter, a mother or a father because of drugs.
"Drugs destroy lives and we need to help people struggling with addiction get healthy through treatment and education. Locking 1,000 drug users up will not help them get clean.
"At the moment, almost four times as many people charged with possession for personal use are sent to prison than are given treatment orders. This needs to change.
"It costs £37,000 a year to keep someone in prison. Unless we focus on getting people off drugs, we will see the same faces going through our justice system time and again. Any way you look at it, we cannot afford to simply write people off.
"We need a sea change in our approach to drug misuse. While other parties try to look tough on crime, Scottish Liberal Democrats are proposing a drug policy based on the best scientific evidence of what works. It is time that we started treating drug addiction as the health issue that it has always been.''
The incident, which happened at Ibrox station, was reported to British Transport Police before 8pm on Saturday.
The jobless rate is 3.9% after a drop of 12,000 in April to June.
The robbery and assault happened in Kilbrennan Drive, Falkirk, at about 5.50pm on Tuesday.
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