Traders in County Durham have warned that children will continue to be used to check on illegal under-age sales.
Over the past six months there have been 66 attempted test purchases of video games, aerosol paint, alcohol and tobacco by child volunteers.
In 13 of these cases the youngsters, aged under 15, were able to purchase age-restricted goods.
Now trading standards officials are going to extend the scheme to cover fireworks, solvents and butane refills.
Phillip Holman, the council's head of trading standards, said: "The use of child volunteers has been a very effective enforcement tool and deterrent in relation to under age alcohol and tobacco sales.
"By extending their use to other age restricted products, we hope to reduce illegal sales, protect vulnerable young people and help reduce incidents of anti-social behaviour.
"Traders and individuals who sell age-restricted products to children risk being taken to court and, if found guilty, could be fined up to a maximum of £5,000 and sentenced to six months in prison."