Leading specialist Dr Nadim Haboubi, chairman of National Obesity Forum Wales, bemoans young children not being involved in activities.
"Children have computer games, iPads and they sit there for hours," he told BBC Wales.
"Unlike perhaps when we were children, there's also a genuine fear it's unsafe for young children to be outside playing, unsupervised.
"They eat too much junk food and now in the school holidays you can see them in burger restaurants from the morning onwards - the places are packed.
"I drive from home to work and there are seven 24-hour burger restaurants but no leisure centres open until late."
"Sweets used to be something you had at Christmas or special occasions, now they're given out as rewards.
"You've got to detect problems at an early age, so it's down to the parents. Obesity can keeping getting worse like a cancer unless you manage it.
"But for those in deprived areas, healthy food is not very affordable either for a lot of people."
Obesity levels are significantly higher than average in Merthyr, Caerphilly and Rhondda Cynon Taf, and significantly lower in Monmouthshire, Conwy and the Vale of Glamorgan.