EVIDENCE is mounting that young children who spend significant periods of time in daycare while their parents work are more prone to developing aggressive and antisocial behaviour.
A new study from the United States suggests that children who went to nursery during their pre-school years rather than staying at home were more likely to be disruptive once formal education began.
The National Institute of Child Health and Human Development (NICHD) has followed the progress and development of 1,300 children since 1991. It concluded that the longer above 10 hours a week a child spent in group care, the more likely teachers were to report difficult behaviour once they started school.
The findings are strikingly similar to the results of a recently published government-funded research project carried out by Oxford University and the Institute for Fiscal Studies.
It concluded that children under the age of three who spend more than 35 hours a week at nursery show higher levels of antisocial behaviour than those spending less time in daycare.
In Scotland, the Executive provides free nursery places for three and four-year-olds, which entitles parents to 12.5 hours care a week.
Almost 99% of four-year-olds take up the places, compared with 96% of three-year-olds. Many parents supplement this with longer-term private care.
The growing demand to balance childcare and work has meant the number of people employed in pre-school education in Scotland has grown to more than 30,000.
The new NICHD research showed that teachers of 11 and 12-year-olds in the US reported that those who spent more time in early childcare were more likely than other children to "be disobedient", to "get in many fights" and to "argue a lot".
This was not reflected in children who were looked after by family members, childminders or nannies.
Teachers involved in the research had a "problem checklist" which they used to rate children on behaviours such as bullying, bragging, arguing, fighting, lying, cheating, cruelty and destructiveness, including arson.
Dr Jim Griffin, NICHD's programme director for early learning and school readiness, believes the low-level negative behaviour may be fuelled by youngsters competing for adult attention in nurseries and childcare centres.
He said: "These findings add to the growing body of research showing that the quality and type of childcare a child experiences early in life can have a lasting impact on their development."
The authors will now continue to follow the children's development in secondary school to see if the effects shown in the current research persist.
The study, the most in-depth of its kind in the world, has tracked the same children at intervals since birth, evaluating their cognitive and social skills, behaviour and academic achievement in the context of their childcare experiences.
Separate research from Cambridge University and the Free University of Berlin found the level of the stress hormone cortisol doubled in some toddlers during their first nine days at nursery.
The levels were still relatively high several months later, even though the toddlers showed no outward signs of distress.
The study, led by Professor Michael Lamb of Cambridge and Lieselotte Ahnert of Berlin, monitored 36 girls and 34 boys aged between 11 and 20 months. The children had all been cared for mainly at home and were then placed in nurseries for 40 hours a week.
Their stress levels were found to be between 75% and 100% higher compared with when they had been at home.
The National Day Nurseries Association felt the research did not give the whole picture. "We hope that families are not needlessly worried by these reports, which only relate to behaviour difficulties in a small number of cases," said a spokeswoman.
"Children from workless households were rated as less cooperative and sociable than children in centres with high levels of working parents. This indicates there is a complex mix of factors that influence a child's behaviour and that careful attention is needed to ensure children are supported appropriately."
But a spokesman for the UK Department of Education said: "Any argument that there is evidence women are letting down their children by going out to work is faintly ludicrous."
A Scottish Executive spokesman said: "We are committed to extending access to high-quality, affordable and flexible childcare services which match children's needs and parents' working patterns."