A psychologist and best-selling author has controversially claimed that even one night away from mum could "reduce brain development".

CHILD psychologists and parenting experts have warned that young children from separated families could suffer brain damage by sleeping over at dad’s if their mum is the primary caregiver.

Psychologist and author Penelope Leach has made the explosive statement that separation from mothers “reduces brain development” and could lead to “unhealthy attachment issues,” according to the Independent.

Dr Leach, whose parenting books have sold millions, says even one night away from mum, if she is the primary caregiver, could cause lasting damage.

Not everyone’s convinced.

@newscomauHQ @louisck That is up there with some of the dumbest advice mankind has come up with. — Adam Peacock (@adampeacock3) June 17, 2014 Sub-type: comment CAPTION: @newscomauHQ @louisck That is up there with some of the dumbest advice mankind has come up with.— Adam Peacock (@adampeacock3) June 17, 2014 Sub-type: comment CAPTION: @newscomauHQ @louisck That is up there with some of the dumbest advice mankind has come up with.— Adam Peacock (@adampeacock3) June 17, 2014

@newscomauHQ @louisck what a disgusting thing to say. My son has been shared care for 11 years he is perfectly fine! He is now 14! — Stewart Nicholls (@StewNicholls) June 17, 2014 Sub-type: comment CAPTION: @newscomauHQ @louisck what a disgusting thing to say. My son has been shared care for 11 years he is perfectly fine! He is now 14!— Stewart Nicholls (@StewNicholls) June 17, 2014 Sub-type: comment CAPTION: @newscomauHQ @louisck what a disgusting thing to say. My son has been shared care for 11 years he is perfectly fine! He is now 14!— Stewart Nicholls (@StewNicholls) June 17, 2014

Dr Leach first caused controversy in the 1970s when she released her book, Your Baby & Child: From Birth To Age Five, which suggested that only mothers could care adequately for a child and a father’s role is secondary.

Dr Leach says shared custody is being treated as a right rather than considering what is best for the child.

Celebrities like Louis CK and Charlie Sheen have spoken about the difficulties faced sharing custody of children. While some may understand how spending a night at Charlie Sheen’s house could be detrimental to his children, Louis CK continually talks about how he would be nothing without his two daughters.

While fathers’ groups have called the comments by Dr Leach ‘absolute poison’, Oliver James, a trained clinical child psychologist, journalist and TV presenter, said Dr Leach was providing “good advice.”

“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 told the Independent. “If the child has a really strong attachment to both parents, there might be a case for exploring whether it really matters if they have sleep- overs at the father’s. But in most cases, you should do nothing to disrupt the relationship with the primary caregiver. To do so can affect the child’s brain development.

“I’m particularly glad Penny is taking aim at the family-law profession, where there is appalling ignorance about these effects on children ... The ruling elite frequently had poor early care themselves – it’s why they are so motivated to get to the top,” he said. “After the age of three, it becomes more debatable about whether children will be damaged by living between two homes and by the age of about six, I don’t think it’s a problem.”

The New Fathers4Justice direct action group, said the advice “sounds like absolute poison and potentially terribly damaging to children’s development”.

“Overnight stays with fathers from as early an age as possible are crucial if children are to form strong attachments with both parents,” a spokesman said.