Just 41 children across England and Wales were given instant fines for underage drinking on licensed premises in 2005, according to Government figures.
Seven under-18s were given penalty notices, which involve fines of £50 or £80, for the same offence in 2004.
Three of the 10 regions - London, the east and the north east - issued no penalty notices at all for the offence in 2005. The North West topped the table with 15 notices.
British Beer and Pub Association director of communications Mark Hastings said: "In discussions we've had with Government we've constantly said it would be very helpful if the law on purchasing was enforced with the same rigour as the law on selling.
"And the industry has to become much better at ensuring its age checks are carried out more rigorously."
National Association of Licensed House Managers boss Dave Daly said: "I don't know why they are reluctant to target underage drinkers. It beggars belief."
Daly called for compulsory education classes on the dangers of drinking for children caught consuming alcohol in pubs and clubs and said the parents of underage drinkers should foot the bill.
The data also shows an increase in penalty notices issued to under-18s for being drunk and disorderly, consuming alcohol in a public place and being drunk in a highway.
The findings were revealed in a statement from minister Vernon Coaker in response to an MP's question.
Final 2005 figures will be available "in the autumn" but the date has not yet been set.