"Childhood obesity is a complex issue," Matthews said. "We don't know what it is we have to do."
The 17-member "Healthy Kids" panel will report with its strategy recommendations by Christmas.
Statistics suggest about three-quarters of obese children grow into obese adults, costing Ontario's health-care system an estimated $4.5 billion in direct and indirect costs.
The problem has been linked to the development of diseases such as diabetes and heart disease in later life.
Overall, childhood obesity rates rose to 26 per cent in 2004 from 15 per cent in 1979, government figures show.
"If we don't take action, the cost to the health-care system will be extraordinary," Matthews said.
Matthews admitted a 20 per cent reduction was a "tremendously ambitious target" but called it critical to tackle "one of the most challenging issues facing Ontario's health-care future."
The panel will take a look at a wide variety of contributing factors, including socio-economic factors, diet and activity levels, as well as at strategies for helping already obese children get back to health.
"I want this to get beyond the common sense and into the science," Matthews said, adding it's important the panel's recommendations be practical and easy to implement.
The panel is being co-chaired by Alex Munter, CEO of the Children's Hospital of Eastern Ontario, and Kelly Murumets, CEO of Participaction.
Munter said society has been successful in the past in affecting positive changes when it comes to illness prevention.
"We have changed the trajectory on health issues as a society," Munter said.
"We've done it on tobacco-related illness, we've done it on the health of mothers and newborns, we've done it on workplace health and safety."
Munter said parents are enormously motivated to raise healthy children, so one aim will be to find ways to help families achieve that goal.
Other panel members include Dr. Denis Daneman, pediatrics professor at the University of Toronto, Dr. Penny Sutcliife, medical officer of health with the Sudbury and District Health Unit, and Phyllis Tanaka, with Food and Consumer Products Canada.