The Beeb has a nice graphic illustrating their article on Generation Next. Below you can see a map coloured to indicate the percentage of people per capita under 18 years of age. Readers of this blog will know that I'm not a fan of this type of cylindrical projection. I'd offer an alternative, but I don't have access to the data that the BBC used to generate the map. The article does credit the United Nations as being the source, but how about a direct link to the data?
As for the data - my reaction is that this distribution probably has an inverted relationship with that of percentage of population with access to the internet.