One big difference between the 3rd world rubbish pit and the school is in the rubbish pit the kids are actually touching, burning and breathing in the fumes of lead while the children in Porkettes school do not have to drink the water to make money to feed their families.
Many older towns and their water supply lines contain lead as does the plumbing inside some older homes, and when the water companies maintain the water supply properly by controlling the waters Ph/ corrosivity level, the lead does not readily leach into the water.
The big awareness of lead in the water supply happened in 2015 in Flint Michigan when the town switched its water source from the Detroit supply to the Flint river. The river may have been more acidic than the treated Detroit supply but according to this article -
http://www.nytimes.com/interactive/2016/01/15/us/flint-lead-water-michigan.html?_r=0
The primary reason the lead started leaching was Flint water supply had a Fecal Coliform bacteria outbreak and added chlorine to the water but did not add anti corrosives to counteract the chlorine.
Chlorine is a very strong, corrosive oxidizer that will rapidly break down other substances, like lead. Had the water "company" added the anti corrosives to the water the lead would still be "safely" in the pipes.
The town has since switched the water source back to Detroit instead of the Flint river and over time the water quality has improved and lead levels are down but the pipes are being replaced anyway as they should be.
http://www.cnn.com/2016/02/19/health/flint-michigan-water-lead-levels-researcher/index.html
The bigger problem will be the homes that have old plumbing with lead in them, the homeowners will have to pay to replace their own plumbing.
Just because your nation, or our nation, has banned the use of lead in many places does not mean you are not exposed to it. Lead is still widely used in consumer products and it is everywhere in our environment because of this and prior wide spread use.
So the same lead found in the rubbish pit is found in the worlds water, soil and air, it is in our food supply, some medicines and folk remedies, electronic consumer goods.
I hate the fact that my favorite treat chocolate contains lead because the countries that grow cocoa still use leaded fuels meaning chocolate contains the more dangerous organic lead not the inorganic lead found in plumbing.
I still eat and enjoy chocolate.