Ruth Kelly's announcement at the Labour Party conference this week that she is giving up her Cabinet post will have sent a frisson of guilt through many working mothers. “I now owe it to my children and family to put them first,” she said. “If I do not, I know it is something I will come to regret deeply.”

No doubt it will make many working mothers think twice about their own choices, as well as thinking: “It's all right for her.” Received wisdom is that children need their mothers most in the first year, and perhaps even until they go to school. But once they're in the thick of it many parents are forced to recognise that school-age children need their mums just as much, in different but equally demanding ways.

Like Ruth Kelly, Julia Bateson gave up a high-powered job, as senior consultant for a database company when the eldest of her four children was 11. Until she had her own Damascene moment, prompted by a teacher asking if she was the new nanny, she had never expected to give up full-time work. “I have always felt the care and attention that babies and little children need didn't have to come from me,” she says, “and that they needed someone very professional; our nanny was much better at looking after them than I was.

“I think it's way more valuable to be at home when the children are older and need more emotional support. The transition from primary to secondary school is a big jump, emotionally as well as academically, and then there are all the crises with friends, spots, that whole 'I'm ugly, nobody likes me' phase, when it's important to understand what's going on and to guide them through. You also need to support them with all the extracurricular activities - and homework: not to put a gun to their head but to guide them.”

Growth and development

Expert opinion differs on when children need their mums most. Karen Sullivan, the author of You Want to Do What? Instant Answers to Your Parenting Dilemmas, and a mother of two teenagers and a toddler, says: “Any loving, caring and responsible person can look after a baby. But as children grow and develop I think they need their parents more and more. Children's morals, interests, social skills and relationships are dictated by the people they spend the most time with. And teenagers require more input than perhaps any other age group.”

But a new report from the Early Years Commission concludes that a baby's “brain formation is crucially dependent on parent-child relationships”. One of the report's authors, Melanie Gill, a child psychologist, believes that in a perfect world mothers should spend as much time as possible with their children in the first four years. She says: “One thing that is missing now is the knowledge that a baby needs its parents hugely. To become an emotionally healthy person a baby needs specific ways of being nurtured. When a baby is born the brain is all in place but it's not “joined together”, and the only way that happens is through relationships - ideally with a parent, and ideally with a mother.”

Choosing to stay at home

Nicola Pharoah agrees, up to a point. She went back to work much later than many of the women in her NCT group, when her son Billy, now 4, was ten months, and she stayed at home for a year after Daisy Mae, 2, was born. “I think from birth to a year babies really need their mothers,” she says. “But between 1 and about 3 it's fine for them to be with a nanny.” Pharoah recently gave up her dream job at Condé Nast (where she was head of video and pictorial content) to be at home full-time when Billy starts school. “I think the children need me more at this stage and that it's important that I'm around from an emotional point of view, to help make them stable, well-educated beings,” she says. “And I'm quite old-fashioned in that I think children need their mums rather than their dads.”

Parents' needs must surely come into it, too: it's not just a cliché that happy mothers make happy children. While some mothers love being at home with little ones, others feel trapped. When Pharoah was at home for a year with a baby and a toddler she admits that she was bored and frustrated: “I felt that I wasn't doing them any good. It's different now. I'm more confident and I'm really enjoying being with them.”

Radical culture change

Of course, the reality is that most parents can't choose to be at home and even working part-time is possible only for a lucky few. Melanie Gill wants to see a radical culture change, informed by an understanding of child development, which would offer parents more choice.

But it's easy to forget that most working parents stretch themselves to the limits to make sure that they are there for their children when it matters. Julia Bateson says: “People think if you've got a nanny you're never there, but of course that's not true.” Kairen Cullen, an educational psychologist, is constantly impressed by working parents' creativity when it comes to helping with homework, for example. “Parents are deeply motivated to support their children,” she says, “but they are not irreplaceable. The idea that it has to be the parent who helps is flawed.”

Karen Sullivan is equally reassuring. “It is obvious that the more time we can spend with our kids, the better we can support them. But the idea of quality time isn't dead, and it is possible to be a great parent as long as parents are regularly there, consistent in their communication and available when children need them.”

Times recommends

• The Boxing Day tsunami: five years on
• What took place in 2010...
• Can you really cure a hangover?