First of all, the infrastructure in big city is much better than in the countryside.There are many highways and long, big bridges which make transportation esier. With so may transport means such as taxi, bus... it is very easy for you to go anywhere at any time. Big schools, big hospitals equiped with modern facilities make the study and treating disease more effective. Living in big cities, children have good opportunities to learn in good schools and examine in good hospitals.
Secondly, in a countryside a child do not really have a chance to get a good education. All qualified teachers and professors live and work in big cities because of better prospectives and job opportunities. If children grow up in a countryside they might never be able to get a good education and thus they will have less chances to get a qualified job in future. For example I have got a friend who grew up in the countryside and moved to HCM after graduating from a countryside University. He had to enter University again because nobody was willing to accept his diploma. Good education may provide a person with a good qualified job which is very important for personal development of any person.
Finally, as a result of these pollutions, the health of most children in city is weak which leads to the various kinds of illnesses. Also crime and different kinds of accidents are making their life in the cities very dangerous , while