Toddlers who spend three or more days a week in nursery are more likely to become anti-social, worried and upset, government research has found.
The amount of time spent in care appears to impact on behaviour
The evaluation of a £370m scheme to expand children's centres found youngsters were more likely to behave poorly the longer they spent in care.
But the report also found 30 hours in care increased children's confidence.
The research comes as teachers warn children are being "institutionalised" by the push to get mothers into work.
The study - A National Evaluation of Neighbourhood Nurseries - assessed the neighbourhood nurseries initiative, which was set up in 2001 to provide more childcare in some of the poorest parts of the country.
The report, carried out by academics at Oxford for the Department for Education and Skills, said: "The 'tipping point' for daily attendance appears to be relatively low in relation to anti-social behaviour.
"When compared with children who attended either one or two days per week, children who attended for three days per week or more were significantly more anti-social."
The number of months in day-care also affected behaviour.
"For the group as a whole, the number of months children had been attending their neighbourhood nursery also had an impact," the study said.
"The longer they had been attending their neighbourhood nursery, the more anti-social they were.
"Further analysis suggested that, when compared with children who had been attending their neighbourhood nursery for less than a year, children who had been attending for 18 months or more were rated as significantly more anti-social."
Mixed age groups
The study also found young children showed more "worried and upset behaviours" when they attended a mixed-age room with children aged four and over.
"In mixed groups, they were more likely to frown, shrug, pout or stamp their feet when given an idea for playing or to be worried about not getting enough attention, or access to toys, food or drink.
The study did find day-care increased confidence and sociability
"Thus, mixed-aged groups may be better for children in terms of cognitive outcomes, but not in terms of behavioural outcomes."
However, the research found the more time children spent each week in day-care, the more confident they were and the more sociable with their peers.
It also found parents using neighbourhood nurseries were highly satisfied with the quality of care provided.
The National Day Nurseries Association (NDNA) said that it was important to recognise that the research findings related to 800 children attending nurseries located in areas of disadvantage.
Chief Executive of the NDNA, Purnima Tanuku, said: "The vast majority of nurseries do have careful behaviour management policies and work closely with parents so that they can help the child grow emotionally."
A spokesperson for the Department for Education and Skills said: "The study also found that good quality provision - better average qualification levels of staff and presence of a qualified teacher, significantly improves levels of social and emotional development and reduces the risk of children developing negative behaviours.
"Our drive to improve skills and qualifications is therefore the right way to tackle this issue."
The research comes as members of the Association of Teachers and Lecturers gave a warning that children who spent all day in childcare lost valuable time with their parents.
ATL's annual conference in Bournemouth is debating a motion which "regrets that the drive towards full employment in an expanding economy will result in a greater institutionalisation of children".