On the eve of Wimbledon, Judy Murray said she was alarmed at the number of obese pupils she met during a recent tour of high schools across the UK.
The tennis coach said more physical education in schools could help cut obesity among children and produce better athletes.
Ms Murray, 52, was touring schools to promote her Set4Sport programme, which aims to improve coordination and grassroots participation in sport.
Last year, she claimed Scotland's young potential sports hopefuls were drowning "in a diet of chip fat served up with an unhealthy dollop of youth and parental indifference".
The tour included stops at the Riverside Museum in Glasgow and the National Museums of Scotland in Edinburgh.
Ms Murray said: "I was doing a fair number of school visits where I was trying to introduce kids to tennis, and I was aware of a significant number who would be overweight and uncoordinated, couldn't throw and catch balls, couldn't co-ordinate their arms and legs at the same time.
"Not all of them, but it seemed a lot more than I had perhaps thought or been aware of when I was growing up."
Ms Murray said PE lessons need to be longer than the accepted 40-minutes, which often involve only 20 minutes activity after time spent in changing rooms is factored in.
She added: "About 20 minutes three times a week is not an awful lot."
She suggested schools be more imaginative in their approach to exercise, offering alternatives such as zumba and aerobics.
Ms Murray also lamented a lack of freedom for youngsters to play outside.
She said: "You can't play football in the streets any more, and a lot of the parks say 'no ball games'. There are a lot more restrictions on what kids can and can't do."
Scotland's Sports Minister Shona Robison said the Government is committed to ensuring at least two hours a week of physical education in primary schools and two periods of PE in secondary schools for pupils in S1-S4 by 2014.
She said: "We want to increase opportunities for children to get involved in sport and physical activity. Exercise is a long-term investment in health and habits formed in childhood and adolescence continue into adulthood,"
She added: "By providing at least two hours of physical education per week we are providing a fantastic platform for young people to better understand the benefits a healthy active lifestyle can bring to them."
Ms Murray created Set4Sport after being inspired by her experience as a tennis coach. It showcases easy ways for parents to play with children and develop skills for sport.
It centres on activities and exercises based on games Ms Murray played with her sons.
In April, Ms Murray, the former head coach of Tennis Scotland, called on politicians of all parties to act now to ease pressure on the Scottish Government's health budget caused by childhood obesity.
The Scottish Government is to make more than £5 million available to local council to help them hit the two-hours-a-week target.
Andy Murray's Wimbledon starts on Tuesday when he plays Nikolay Davydenko.