One of the main drivers of Chinese immigration in the late 19th and early 20th century into Thailand was famine in China. They knew they could never starve in Thailand.
It is very sad that a child has died. However the underlying reason for his death was not a lack of food. There is absolutely a huge part of this story missing. Could be sickness, maltreatment, very strange parental beliefs, anorexia or many more. Until there is a thorough investigation, the reason will not be known.