In the case of Africa there are at least two reasons.
1. Many of them are of a Roman Catholic tradition, and even though their circumstances are dire, the Vatican will not sanction the use of any form of contraception.
2. They are of a similar mindset to British people of the Victorian age, in that they want to have children to take care of them when they are older, and have 4 or 5 kids in the knowledge that at least a couple of them probably wont survive to adulthood.
So the best aid we can probably give them is an enlightened education and an endless supply of condoms.
As for the TV advertising charities. They are a sector of the economy, with all that this implies. They usually have the infrastructure of a medium to large PLC, with directors salaries to match, and huge pension fund liabilities for past and present employees.
I would dearly love them to be compelled to publish very detailed and transparent accounts of where their money goes.
Ian Botham resigned from the RSPB a few years ago, after a lifetime of support when he discovered "It is a pension fund, with a charity attached to it."