When Katie noticed that her son Jack was sitting with his legs folded underneath him in a 'W' shape she didn't think much of it. "I'd seen other kids sitting that way, so I just assumed it was a toddler thing and nothing to worry about," she recalls.
But when a preschool teacher noticed Jack favouring his left leg when jumping and getting up from the ground she warned Katie that there could be an issue with his mobility. That's when Katie learnt that it's called W-sitting, and that it can be a problem.
Experts call it 'W-sitting' for an obvious reason – when you look from above, the child's legs look like a 'W'. Their bottom is on the ground and their knees are bent in front of them, with their feet tucked under them or splayed out to the sides. But is it a cause for concern?
Marianne McCormick, the head of physiotherapy at Sydney Children's Hospital in Randwick, notes that W-sitting can put a child's hips into an in-turned position, which puts pressure on their shins and feet.
"Some children adopt this posture because they lack the strength and muscle control to support themselves in sitting with their legs in front of them," she says.
While lots of kids do it occasionally, there is a risk that children who spend too much time in the position will become pigeon toed.
"The lower limb alignment of children changes with their growth. This is a normal process. Most babies and toddlers have 'bandy' legs, and this progresses to being a bit 'knock-kneed' when they're three to seven, before ending straight when they are eight or nine," McCormick says.
"W-sitting can continue the 'knock kneed' phase of their development, preventing the normal development of the shape of their thigh bones and hips," McCormick explains.
McCormick notes that W-sitting is common in kids who are really flexible, or hypermobile.
So what should you do if you see your child sitting in the 'W' position?
"Physiotherapists would like to see the development of skills in lots of different positions. Try to encourage sitting with legs crossed in front, to counteract the in-turning force," says McCormick.
"This can be done by positioning your child for longer periods, for example when they are watching TV, reading a book with you or having a snack."
McCormick stresses that it is unrealistic to for parents to correct W-sitting every time it happens.
However, she says that if the in-turning of the hips becomes so severe that the child is falling over, it is best to seek a review with their GP or a paediatric physiotherapist.
In many cases, W-sitting isn't much to worry about. But sometimes it can cause problems.
For Jack, years of W-sitting led to a 'lazy bum cheek'. Despite trips to the physio and specially prescribed exercises, Katie says it can't be corrected.
"His walking is fine but if you look closely you can see it when he runs – he leads with his toes and the balls of his feet, so he's always tripping over," she explains.
For other mums, W-sitting is just one of the quirks of early childhood.
Kerry noticed her daughter Harriet sitting in a 'W' around the time of her first birthday. Knowing that it can cause mobility issues, Kerry opted to move Harriet into different sitting positions.
"I wasn't worried at all though, and she seems to be growing out of it now," she says.