"They are sweetened by pineapple juice concentrate and honey. And pineapple juice and honey will rot your teeth just as much as cane sugar will," he said.
Otago University dentistry professor Bernadette Drummond said the biggest risk was that children might sip from the pouches over a long period, keeping the sugary yoghurt in their mouths.
"The biggest problem for tooth decay is that if children sip it goes on and on. You are feeding the bacteria," she said.
"If you eat it all at once, your saliva can undo the damage that is done. The slogan is: give your teeth a rest."
New World Health Organisation guidelines last year recommend keeping "free" sugars below 5 per cent of daily energy requirements. In New Zealand, this means a maximum of 23.5g or six teaspoons of sugar for adults, and 22g or 5.5 teaspoons for an 8-year-old child.
"Free" sugars are those added during cooking or manufacturing and include sucrose (table sugar), glucose, fructose, honey, syrups, fruit juice and fruit juice concentrates.
This excludes naturally occurring sugars such as those in fruit and milk. Plain blue-top milk, with no added sugar, has 4.8g of a natural sugar, lactose, accounting for almost half of the total sugar in a honeycomb "spouch".
Some other yoghurt pouches have slightly less total sugar than the honeycomb spouch. Fonterra's Anchor Uno strawberry yoghurt pouch has only 9.9g of total sugar in 100g. The Collective's Moogurt and Vaalia are 11 per cent sugar.
Beaglehole said popular children's cereals had much more sugar. A Kellogg's cereal branded with the Disney children's movie Frozen is 22.2 per cent sugar, more than Tip Top Neapolitan ice cream (19.4 per cent).
"I put icecream on the breakfast table in front of my kids with the Kellogg's Frozen cereal and said, 'Which one would you like'?" he said. "They both said they'd take icecream, so I let them because there was more sugar in the breakfast cereal than there was in ice cream."
Muesli bars, a common item in many school lunches, can have even higher sugar content. A Mother Earth baked oaty slice clocks in at 29.1 per cent sugar.
Auckland paediatric dentist Dr Nina Vasan says her 9-year-old daughter Sasha Situe has become a big fan of the "suckies" since they came on to the market about 18 months ago.
"For most children, the novelty of sucking on the pouch at school is what they really want, and to have the same as other kids in their lunchbox. I think it's actually a bit of a fad."
Dr Vasan said she would rather Sacha ate a yoghurt "spouch" than "a sweet sticky muesli bar that is going to stay in the mouth for a lot longer".
She ensured her child consumed the pouches in moderation.
"The yoghurt suckies are fine for children to consume occasionally," she said.
"Being a busy working mum, I buy them for my kid's lunchboxes sometimes.
"However, they need to be sensibly consumed, to reduce the risk of tooth decay from the sugar content. The more frequently they are consumed, the higher the risk of tooth decay."
Angus Allan, a chef who co-founded The Collective in 2009, said the sugars in the company's pouches were all "naturally occurring in milk (lactose), fruit (fructose) or honey".
"Our product range includes foods that are a 'sometimes' or treat food, right through to products that can be enjoyed every day such as our Straight Up yoghurts that are unsweetened," he said.
"We do not encourage excessive consumption or sucking for long periods of time."
