Infant mortality is high in these countries, ergo the more kids you have the more chance you have of some surviving to adulthood.
There is no welfare there at all, so when you are old and frail you will need someone to look after you.
We in Britain will have to utilise the same solution, the provision for care to the elderly is very poor and expensive, the cost of living now is very expensive, job security is poor (casual work, agency work, fixed term contracts etal), pensions are decreasing in value whilst the abilty to save (see above) is hugely diminished.
One cannot save for jam tomorrow when one needs bread today.
Pensioner poverty in the years to come will be almost Dickensian, and not all due to fecklessness.
So ask yourself, if you have one or two children and you have to go into a care home at £500 a week that's a large chunk of money out of their pockets (especially if they have children of their own) so whose gonna pay?
The state?
Don't count on it, if you have four or five kids the state will help you to feed and clothe them, give them medicine, then when you are old between them they can pay towards your care in a more manageable amount.