There is no evidence of ill-effects on children's social and emotional behaviour if their mothers work during the early years, a study suggests.
University College London researchers studied data on 12,000 children and said the best arrangement was where both parents lived at home and worked.
Girls whose mothers did not work showed more difficulties at age five than those with employed mothers, they said.
Other studies show children of working mothers are more likely to be obese.
The new study examined information on the children over a period of five years - although it was limited to those whose ethnicity was classed as white.
Mothers were asked to report on behavioural issues such as hyperactivity, aggression, nervousness, clinging, and difficulties relating to peers affecting their children at the ages of three and five.
The study, funded by the Economic and Social Research Council, then compared this information with data on who was working in the child's household, as well as on income, education and whether the mother was depressed.
Lead researcher Anne McMunn told the BBC that some of the findings were partly explained by the fact that mothers who worked were often better educated, in households with higher incomes and were less likely to be depressed.
But even when these factors were taken into account, no detrimental effect of mothers working could be seen - at least within two parent families, she said.
And girls whose mothers had not been in the labour force at all were still twice as likely to have behavioural difficulties at age five as those whose mothers had worked throughout, she added.
The researchers observed that this "may reflect the importance of gender in family role model processes".
This finding remained "unexplained", Ms McMunn said.
"Maybe there's something about girls in particular seeing their mothers going out to work - participating in society and playing an active role - that is good for them... we don't know," she added.
The study also found that boys in homes where the mother worked but the father did not were more likely to have behavioural problems.
But this could be explained by factors such as income and education, Ms McMunn said.
She said that the findings may have been affected by the fact that the observations on children's behaviour were made by mothers, and working mothers may have answered the question slightly differently from those not in the labour force.
The researchers noted that existing studies on the impact of mothers working, particularly in the early years, show "mixed results".
Several studies have shown that children of working mothers are more likely to be overweight, have poor diet and sedentary lifestyles.
Dr Katherine Rake, chief executive of the Family and Parenting Institute, said: "The fact that no evidence was found to show working mothers restrict the early development of their children is welcome news.
"This study shows what mothers know intuitively - if you are able to get the balance right, your child and your career can both flourish."
Sally Russell, co-founder of the Netmums social networking website, said 62% of the site's members were in full or part-time work and many worried about the effect on their children.
"Previous research that suggested working has a detrimental impact on children added to the pressure, so this latest study will be reassuring and very welcome news for all those millions of working parents," she said.