Seven in 10 parents know youngsters should consume five portions of fruit and vegetables a day, but 29 per cent admit having no knowledge of the reasons behind this requirement.
A fifth were also unsure of the ways to boost vitamin D levels, and more than 15 per cent felt the same about increasing vitamin C for their child.
The Department of Health recommends all children aged six months to five years are given vitamin supplements containing vitamins A, C and D every day, but 43 per cent of parents are unaware of which vitamins their children are advised to take.
Vitamins expert Parminder Kaur warned of an overload of information online that could be distorting the messages of health professionals to parents.
“While sources like the internet have made lots of information available, there is also a lot of disinformation out there which can be hard to filter out,” she said.
“So, it’s not surprising there is confusion around how much we need of certain types of vitamins, or even where to get them from.
“This can be especially difficult for parents, who have to find the balance between what their children will actually eat, and then work out if it’s good for them or not.”
In the poll of 2,000 parents carried out by Boots Kids Vitamins, four in 10 were able to identify vitamin C as something that helps absorb iron into the body and supports the immune system.
And just one in 10 were able to name the recommended daily dose of vitamin D, which is just 10 micrograms.
Twice as many people believe the suggested amount is 10mg – which is 1,000 times more than advised.
Vitamin A – also known as retinol – is mainly used in the body to maintain healthy skin and eyes, but millions of Brits were unaware of this.
The study also found one quarter of British parents worry about the levels of nutrition their children are getting, with 56 per cent giving their children a vitamin supplement product.
But of those that do not, 10 per cent worry supplements contain too much sugar, and a further 28 per cent are unsure of where to start with purchasing them.
Ms Kaur added: “All parents would agree it’s vitally important to make sure your child grows up eating the right things.
“Whilst children should be able to get all the essential nutrients they need from diet alone, sometimes they can be fussy with their diet, which is where a vitamin supplement can come in handy.
“Even if you think your children get a generally healthy diet, you may wish to consider a general multivitamin as a way of filling in any nutritional gaps they may have.”