A 14-year-old buys a knife in a high street store.
No one was jailed for selling a knife to a child in England and Wales in the five years up to 2006, it has emerged.
Most of the 71 people convicted of selling knives to under 16-year-olds were fined, but mostly less than £500, despite the maximum fine being £5,000.
Only one person was given a community sentence, despite the maximum sentence being six months in prison.
The figures, up to the end of 2006, were revealed following parliamentary questions by the Liberal Democrats.
Last year the ban on selling knives was extended to under-18s, but these figures are not yet available.
'Pitiful'
The Liberal Democrats described the fines imposed as "pitiful" and called for tougher penalties to send a message that selling knives to children is "unacceptable".
The ways in which young people obtain knives has come under increase scrutiny in recent months in the wake of several high profile stabbings involving teenagers.
Research suggests the age of knife crime victims has been falling, with 17 teenagers in London alone having died from stab wounds since the start of the year.
But analysis of official data shows the number of people killed with a sharp instrument across the UK in the 10 years to 2006 has remained stable at about 200 annually.
BBC Home Affairs Correspondent Danny Shaw said Justice Minister Jack Straw had set up a review of knife crime sentencing, to make sure the system was clear, proportionate and working effectively.
The legislation covering sales is enforced by council trading standards officers. Test purchases are commonly carried using underage volunteers.
Meanwhile, under new guidelines for police and prosecutors, anyone aged 16 or over in England and Wales who carries a knife could be taken to court.
Previous police guidance was to prosecute adults caught with a knife, but to caution those under 18.
Conservative leader David Cameron says the presumption should go further - so anyone convicted of carrying a knife should be jailed.
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