About 800,000 parents in poorer families will get free fruit and vegetables through a voucher system announced yesterday by John Reid, the health secretary.

He said the government plans to extend the welfare food scheme, first introduced as a wartime measure in 1940, to fight a new battle against childhood obesity.

Families in England with children over one year-old will receive vouchers worth at least £2.80 a week, and those with children under one will get £5.60. They will be able to exchange them for fruit and vegetables at greengrocers, supermarkets and other outlets.

All pregnant women under 18 will also be eligible, regardless of family income.

Mr Reid said the move was aimed at improving the nutritional balance among young children in poorer families. It followed a report last week by medical royal colleges and the faculty of public health warning that 9% of children between two and four are obese.

The plans are to be introduced through a reform of the welfare food scheme, introduced in 1940 to protect children's health by providing free milk during the second world war.

The scheme still provides milk tokens to the poorest pregnant women and families. These will be replaced with weekly vouchers for fresh produce as well as milk, available to families on low income. Children in nurseries will also be offered a choice of milk or fruit.

Mr Reid said: "The best way of tackling obesity is through encouraging healthy diet at an early age. These changes mean that pregnant women, nursing mothers and younger children will have a greater choice of healthy eating options."

The changes will be phased in from the end of the year.