The Government may consider changes to the laws banning children from pubs after 9 p.m. if evidence shows that it has damaged the tourist industry, the Minister for the Environment, Mr Cullen, has said.
However, the Department of Justice, Equality and Law Reform has insisted that Mr McDowell has no plans to alter the licensing law change and does not accept that it has had "a major impact" on trade.
On RTÉ's Saturday View, Mr Cullen, meanwhile, doubted publicans' claims that the restriction on children, along with the smoking ban, were responsible for the fall in business experienced in some areas this summer.
But he said: "You try these things to see if they do work and if they do have the effect which they set out to, which is to curb under-age drinking, then good.
"If they are not making a difference in this regard but are having a major effect on one of our major industries, then, obviously, any government has to be realistic and look at that and see where the balance lies in achieving the ends.
"There is always room for manoeuvre. The Government is not there trying to stop people enjoying their lives or trying to change the face of Ireland to make it something different. There is a learning by doing," he said.
Opinion poll research, he said, showed that 89 per cent of the public was in favour of keeping under-18s out of pubs after 9 p.m., even if accompanied by adults.
The legislation does not prevent children being in restaurants, or any part of a premises not containing a bar after 9 p.m.
Publicans, he said, faced "major difficulties" trying to identify under-age drinkers, particularly those aged between 16 and 18.
Backing a compulsory national identity card, Mr Cullen said: "This is something that is long overdue in Ireland. It is interesting that every time we go to do this in Ireland, the liberal wing starts to say that we are interfering in people's rights.
"It isn't. We should have a proper ID system in this country where everybody carries a proper ID card," the Minister said.
Criticising Ireland's drinking culture, he said the "atmosphere" in pubs influenced children because they saw their parents and other adults drinking, and were open to the advertising of drink companies.
"We need to row back strongly on this over-emphasis on alcohol, where it is at the centre of everything. We will reap a whirlwind in the years to come," he said.
During a recent holiday with his own children, the Minister said that they had "not been in a pub once and we did not feel the need to do so".
Teenagers were now under ever-increasing pressure to start drinking, he said, encouraged by the advertising behind alcopops that were "an appalling abomination".
A spokesman for the Minister for Justice, who is currently abroad with his family on holidays, said Mr McDowell remained committed to the 9 p.m. ban
"The Minister has already said that if anyone has any proposal that will have the same effect - reduce the amount of underage drinking - that he would be prepared to consider them.
However, she said, the Minister "does not accept" that the 9 p.m. ban had had "a major impact" on the licensing trade since its introduction.
Though downplaying the possibility of a change, the spokeswoman said amendments could be made, if necessary, when the Minister brought codification legislation, bringing all of the country's licensing laws into one piece of law, in the autumn.