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Advertisements for a kids' movie have been reduced to the size of a finger nail and plastered on nectarines.

Stickers on the fruit show Yogi Bear smiling and waving, a promotion intended to reach children at picnics and draw them to the cinema - to watch a movie full of picnic scenes.

Otago University marketing professor Janet Hoek said it was the first time she had seen fresh fruit marketed in such a way, fast-food chain McDonald's often had tie-ups with children's movies, such as Shrek.

Dr Hoek said such campaigns raised ethical questions about encouraging children to associate happy times with products in ways they did not understand.

Advertising on fruit was "unexpected". A rare example was a road safety campaign where stickers on watermelons invited consumers to drop the fruit to get an impression of how people looked in high-speed crashes.

"In the road safety case, it's possible to argue the shock value of the comparison justified the unexpected medium," Dr Hoek said.

"These arguments would not apply to the current case, which has no social outcome but is simply trying to stimulate children to go to movies."

Although ads on fruit are novel, other healthy foods, such as yoghurt and Kraft cheese, have previously been promoted with movie characters.

Most controversy has been about fat and childhood obesity, but some critics have objected to advertisers trying to manipulate children.

The stickers on nectarines from the Yummy Fruit Company, as well as product information have a picture of Yogi Bear, the movie logo and a tiny blurb reading, "In Cinemas 13 January 2011".

Simon Renall, of Yummy Fruit, said the promotion was a first for the company but Yogi Bear was a good match because of its picnic basket motif.

Mr Renall said the promotion was similar to its other campaigns where children collected stickers to get prizes.

Green MP Sue Kedgley said nobody liked having stickers on their fruit, and it was worse if they were ads.

"Most consumers find stickers on fruit irritating," Ms Kedgley said.

"If we're going to have to have stickers on fruit, at least give us information, such as where the product comes from, rather than try to promote a movie."

Food and Grocery Council chief executive Katherine Rich said the promotion could be a fun way to get children to eat more fruit.

"Some food activists forget food is meant to be enjoyed. It's a fun way to get children to eat more healthy food." Her children had noticed the Yogi Bear stickers after they saw the movie and took to eating more nectarines.

"It's become a popular choice in our house since the stickers. It brings smiles to faces."

It could also help fruit marketers, who struggled to make their products stand out at supermarkets.

The food sector continually debated about using children's movie characters on packaging, Ms Rich said.