Some yoghurts contain almost all of a child's recommended daily sugar intake
Apparently healthy yoghurts can come close to sending children over their daily sugar limit in a single helping, campaigners have warned.
Public Health Liverpool said its own analysis found that some yoghurts contain the equivalent of almost five sugar cubes.
NHS guidelines say children aged between four and six should have no more than 19g or five cubes of free sugar (sugar not 'locked in' naturally to products) a day, while seven-to-10-year-olds should have no more than six cubes.
Public Health Liverpool is to highlight its findings with a media campaign across health centres, dentists' surgeries, children's centres and hospitals over the coming months.
It is also launching a roadshow tour of supermarkets and public buildings where experts will be available to talk to caregivers about healthy food choices.
The drive, which is backed by the Liverpool-based campaign group Food Active, is aimed at tackling childhood obesity in the city, where figures show around 12% of school reception age children and more than 23% of year six pupils are classed as obese.
Almost a third of five-year-olds in Liverpool have decayed, missing or filled teeth, with two children a day under the age of 10 having to be admitted to hospital to get teeth removed.
Councillor Tim Beaumont, mayoral lead for wellbeing, said: "Parents are bombarded by marketing messages that yoghurts are healthy. Some are, but many are loaded with sugar and families simply don't realise how much is in them.
"We're not trying to say 'don't eat that', we're trying to present people with information in a way that's easy to understand, so they have a choice.
"Combined with other sugary snacks, drinks and chocolate bars, yoghurts are contributing to an alarming level of tooth decay and obesity in children."
Dr Sandra Davies, Liverpool's director of public health, said: "Tackling sugar in diets is a real priority for us because we know that people simply don't realise how much they are consuming.
"If we are to stand any chance of tackling this ticking time bomb, we must give parents as much information as possible so they can make informed decisions.
"Most people don't have the time to read labels when racing around the supermarket to complete their weekly shop, and so we have to support them to make healthier choices."
Beth Bradshaw, from Food Active, said: "The issue with fruit in a lot of pre-packaged yoghurts is that it has been processed and altered to be almost unrecognisable.
"Yoghurt is such a healthy and delicious food to give children. It should feature in their diet on a daily basis because it's full of calcium, which helps promote healthy bone development and is a really good source of protein.
"The golden rule is to opt for plain yoghurt as a starting point - plain low fat Greek and natural yoghurts are delicious and are much lower in added sugars. Plus you can add in your own tasty fruit flavours just the way your child likes them."
The number of sugar cubes in popular yoghurts, as analysed by Public Health Liverpool:
4.9 - Muller corner
4.7 - Aldi Brooklea (own brand)
4.5 - Asda own brand
3.3 - Smarties (Nestle)
2.6 - Ski (Nestle)
2.2 - Lidl Milbona (own brand)
2.1 - Petits Filous (Yoplait)
2 - Munch Bunch (Nestle)
Each cube = 4g of added sugar