To start with, this problem already occured in many countries. It is already a common problem in high developed countries, for example USA. I managed to analyse the reasons andcame in with some ways to somehow solve this problem or at least do not let it spread more.
As I mentioned in the introduction, both childhood and adult obesity is usually a problem in high developed countries. This statement may cause some questions though. Obesity is a bad thing, why does it appear in high developed countries? The answer and the main reason is the increase in quality of life. It is also a bit controversial, but with the better living conditions, people earn more and are able to buy more food. And they are most likely to buy some delicious yet unhealthy food, and also buy more than they need. With the growing fastfood companies around the world, even people who are not earning a lot of money can acquire those unhealthy meals at for example McDonalds or Burger King. And of course these companies are more interested in having their food spots in highly developed countries, where people tend to both earn and spend more money. And of course, it also applies to the children. Small children are not that smart yet to understand the consequences of their actions. So when they receive some pocket money from their parents, they will most likely spent it one some things that are not very good, including some fastfood.
It is very hard to prevent the increase of obese kids nowadays. Many people are already relying too much on fastfood, in addition new spots are opened every day. But parents can do it! They can simply do not give them fastfood till they will reach a certain age, and feed them well at home, so they will not think to eat some unhealthy food outside. Parents can also talk to their child about some sport activites, sports are both fun and healthy. I have many a few ideas how governments should react on this problem. They may organise some sport events, build the facilities for that and so on. Governments can apply taxes to fastfood, make some restrictions, but it might lead to protests, specially from those group of people that already rely on fastfood too much, or simply have no other choice to buy other healthy food, which also may be quite expensive.
In conclusion, parents are the ones who should control their kids, and prevent them from overeating or frequently eating unhealthy food. And of couse if the parents themselfs do sports and do not eat much fastfood, their kid tends to follow some of their good habits.