A funny portrayal of a "cool dad" in a television ad about under-18s drinking has won praise for challenging parents' thinking on how they should behave at young people's parties.

The central character in the advertising campaign is a middle-aged dad trying to be the life of the party among youngsters with his '80s dance moves, dolphin dives, clinking of lager bottles and skateboarding.

He is handing out "frosty beverinos" to mates of his under-18 teen and trying to engage them in a cool way but failing dismally, says Tane Cassidy, the general manager of the Health Promotion Agency, which is running the campaign.

"Those at the party reinforce the message that our cool dad really isn't cool, which emphasises the point that this is not what you do."

A voice-over goes on to explain the law change from Wednesday which limits young people's access to alcohol and puts more responsibility on those who give them liquor, while giving parents more control over their kids getting drink away from home.

In addition to the television commercial, there are press and radio advertisements and online advertising - extending the "cool dad" theme to "cool older brothers" to tell over-18s that it will be illegal for them to give liquor to under-age siblings.

Online banners also appeal to "cool sister" and "cool mum".

Mr Cassidy said the challenge for campaign agency DraftFCB was to engage with an audience who might have been turned off by a more boring announcement of a law change.

Making a commercial that was fun and entertaining had been tried with success in the Health Promotion Agency's campaign to "ease up on the drink" which introduced the terms "Say Yeah Nah" and "No more beersies for you".

The "cool dad" commercial brought praise from John Cowan, of The Parenting Place.

"I think it's a great advert because it subtly points out the tendency for parents to want to be accepted by their teenagers as a peer rather than a parent.

"Teenagers have enough mates. They just need more parents in their life," said Mr Cowan.

"When we flirt with their girlfriends and try to impress and win their friendship by plying them with alcohol, we just look pathetic in the teenagers' eyes and lose the sense of authority."

Mr Cowan said the serious message in the commercial was that too many teenagers get alcohol from the people who should be protecting them from it.

But the fun in the commercial and its appeal to a sense of shared embarrassment made people think whether it was how to behave and if they should show more maturity.

The DraftFCB creators of the "cool dad" commercial were Matt Williams and Freddie Coltart.

Mr Williams said:"We wanted mums and dads to see that ad and say: "I don't want to be like that guy; by providing alcohol, I'm potentially trying too hard - like cool dad."

Under-18s alcohol law

• From Wednesday, changes to the Sale and Supply of Liquor Act make it illegal to give under-18s alcohol without parental consent and the alcohol must be supplied in a responsible manner.

• The person supplying the alcohol must be either the parent or legal guardian or have express consent of a parent or guardian.

• Consent includes a phone conversation with the "supplier", handwritten note or text message.

• You could be fined up to $2,000 for breaking the law.

• See alcohol.org.nz for more information.