A lot of countries already ban packs of less than 20 to reduce the incidence of children smoking (Malaysia still sells packs in 7s). A ban on smaller packs has not shown a direct reduction in children smoking, as there are so many other factors and what often happens is children pool their money, or that one child buys cigarettes and sells them individually to others.
Banning vending machines may make a difference. In Germany they used to be on every street corner, but not now (and the old Marl used to be the same size as an old 5p, so a pack of 20 could be obtained for 20p!)
Thailand recently banned the display of cigarettes, it is too early to say what the impact will be. As I ex-smoker, it would not have deterred me once I was smoking. However, if all these measures make smoking less cool for kids, then if may help. However, more regulation tends to encourage more rebellion!