When Vicky Howard and her husband divorced last year, she was all for their 18-month-old daughter, Molly, spending every other weekend with him. But a year later, she would do anything to stop Molly spending nights at his flat.
"I'm not saying he shouldn't see her. But as for staying the night, I think it's harmful. She comes home out of sorts and I wonder what all the to-ing and fro-ing will do to her in the long term."
Vicky is not alone, with thousands of single mothers fearful about the effects on their young children of going for sleepovers at their dads.
"I'm really concerned, but people have told me it's politically incorrect and selfish to think like that and my ex's lawyers would surely laugh me out of court, so I generally keep my worries to myself," says one mother of a two-year-old, who wishes to remain anonymous.
One of Britain's leading parenting experts, Penelope Leach, says these mothers are right to be worried.
In fact, the psychologist, whose parenting books have sold millions, has made the controversial claim that children aged four and under should not be having sleepovers with their fathers at all when couples have separated.
In her new book, Family Breakdown, Leach claims that attempts by separated parents to 'share' young children is putting adult rights above those of children and that there is undisputed evidence that separating children from their mothers reduces brain development and creates a tendency towards unhealthy attachment issues.
"When people say that it's 'only fair' for a father and mother to share their five-year-old daughter on alternate weeks, they mean it is fair to the adults – who see her as a possession and her presence as their right – not that it is fair to the child," she says.
Leach, who has previously caused controversy by claiming that only mothers can care adequately for their children and that the paternal role is only of secondary importance, also took the opportunity to have a stab at the legal profession.
"When a lawyer bids for his client to have his baby or toddler to stay overnight each weekend, they are both ignoring clear evidence that such overnight separations from the mother are not only usually distressing, but also potentially damaging to the brain development and secure attachment of children under about four."
Clinical child psychologist Oliver James couldn't agree more.
"All the evidence suggests that younger children should not be separated from their primary caregiver who, in the vast majority of cases, is the mother," he says.
"My only reservation would be if the child genuinely had as strong an attachment to the father as the mother before the break up, but this is unusual."
James particularly welcomes Leach's criticism of the family law profession, which he believes has 'atrocious ignorance about the damage to children of decisions they make.'
"The Government could rectify this but doesn't," he says.
Even some fathers believe Leach has made a valid point.
"I split up with my wife four years ago, when our twins were three and it seemed to upset them terribly being moved about," says Paul Adams.
"They would cry and cry over things like not having all their teddies around them, but we felt it was the general disruption that was bothering them. So we decided to wait a few years to resume sleepovers at mine, which we've now done slowly and successfully,"
But others are outraged by Leach's comments. A spokesman for New Father's 4 Justice group says,
Arguments in favour of mother-only parenting are based on outdated views that females have some kind of inbuilt instinct that makes them better parents than men, he adds.
"In any case, single mums deserve a break," points out Paula Hall, author of Help Your Children Cope With Your Divorce and spokesperson for Relate.
"Who better for the child to go to than the father? Are we saying kids should never go to stay with grandparents either?
"This is scaremongering, as well as being both unfair, unhelpful and divisive for couples. Parents carry enough anxiety and guilt around separation as it is. Why on earth would we want to add to it?"
The second most important factor that can damage children following divorce or separation, according to research, is lack of access to the non-resident parent, she says. "Again, this ban would only add to this lack of access."
For Ian Ashford, Leach's comments will be yet another reason for his wife to try and deny him access to their 13-month-old daughter, he says.
"We both love our daughter and she's attached to both of us, but my ex-wife seems to want me out of the picture altogether and she'll be rubbing her hands together at this. I have a friend in a similar situation."
Leach's comments are a bit like saying that a mother should never go out and allow Dad to put the children to bed, concludes Elizabeth O'Shea, a parenting specialist who runs parenting courses in deprived areas of London.
"In my opinion, if parents separate, the earlier a child can get used to staying with both Mum and Dad, the better. In fact, I truly believe that it is psychologically damaging to refuse to allow a child to have overnight stays with him."
Children need to be allowed to have a childhood, free from having to choose between their parents, she argues. "Children are adaptable."
But Nick Woodhall, author and practitioner at The Family Separation Clinic, believes it's not that black and white.
"I actually think it's quite a good thing that Leach has drawn attention to the impact on children of having to spend time in two homes because it can be tiring for children to move around every few days," he says.
"Research shows that even with tiny infants, even a change in washing powder can be disruptive because the house smells different."
But it doesn't follow that kids should never get to have sleepovers at their dads, he insists.
"There are good reasons for it to happen. It's just that kids sometimes need help with managing the shift from one household to another. If we can take anything from this, I think it should be focusing on this middle ground."
More on Parentdish:
How to host a stress-free sleepover
Sleepovers: Sweet dreams or midnight mayhems?