A moment before this photo was taken in 1998, this boy was playing with his friends. The can of Coke was empty but he kept clinging to it. Simple pleasures and luxuries that we take for granted are far more special to people in Vietnam.
Vietnamese people don't enjoy potato chips or most forms of North American junk food although that is slowly changing. When I first visited in 1996, there was no such thing. They now have their own versions of shrimp flavoured chips and other high calorie foods although home made food treats such as rice/bean/coconut snacks are still the most commonly sold. However, Coke has an amazing ability to sell even when people cannot really afford it.
Although this boy was not asking for money, it is an extremely common sight to find children begging in the marketplace. They look much worse off than this child. Often, children are leading a blind or disfigured parent around, assisting them in begging for money. Sometimes you will see the reverse ... an adult taking a disfigured child around to beg for money. Keep in mind that often, these children are being exploited and the proceeds will never be used for the child. I have heard that some unscrupulous people will even "rent" their disabled child out so they can be paraded around to beg for money from tourists.
As mentioned, it is common to see people with missing limbs and birth defects. They are usually remnants of the war between the North and the South which ended quickly in 1975 not too long after US Forces left the country. Birth defects were often caused by chemicals such as "agent orange" dropped by US planes.