The government is investing an additional £30m on an untested health visiting scheme that will reach too few needy families, according to trade unionists.
Health minister Ann Keen announced the extra funding at Unite's annual professional conference in Torquay last week.
The money will be spent on expanding the family nurse partnership programme, in which disadvantaged young parents are regularly visited by nurses to build their parenting skills and adopt healthier lifestyles.
Ms Keen said: 'Children at risk of social exclusion in later life need intensive, preventive early intervention to improve their life chances.
'The programme is proving popular and is taken up by 90 per cent of the hard-to-reach families that it is offered to.
'It has also been welcomed by the health visitors and midwives who are seeing positive changes take place in behaviour, relationships and well-being.'
However, the Community Health Practitioners' and Health Visitors' Association, which is part of Unite, is sceptical about whether the scheme will work.
It claims it will only help the most vulnerable 2 per cent of families and is not yet properly evaluated.
The association's and Unite's health sector acting lead professional officer Cheryll Adams said: 'Health visiting needs to respond to the public health priorities of the UK population - and not one necessarily based on an imported American model.'