Half of the sugar young children in England consume comes from unhealthy snacks and sweet drinks, figures show.
On average, primary school children have at least three sugary snacks a day, Public Health England found.
This means they can easily consume three times more sugar than the recommended maximum.
PHE has launched a campaign to encourage parents to look for healthier snacks of no more than 100 calories - and to limit them to two a day.
The eight-week Change4Life campaign will offer money-off vouchers towards items including malt loaf, lower-sugar yoghurt and drinks with no added sugar in some supermarkets.