Food is a basic part of life. Nowadays we can prepare meals much faster than we could in the past. Microwave ovens and other kitchen appliances made it possible. But to my mind these technologies can cause more harm than good.
With chemical substances microwave ovens prepare delicious food quickly. Of course that's bad for our health.
The second reason why children are overweight is GM foods. Nowadays with modern bio technology scientists can give plants and animals any property they want. It also destroys children's health and may cause fatness.
But I believe the main reason why number of children are overweight is that fast food companies are very common nowadays.
We live very fast lives and sometimes parents don't have enough time to do meals, so they give their child money to buy food outside. Eating junk food frequently can cause different diseases and fatness too.
It's flagrant necessity that modern kitchen appliances, GM foods and fast food is bad for health. They also cause fatness.