Every year about 9 million children die before they can celebrate their fifth birthday. Two-thirds of those deaths stem from preventable causes that have relatively low-cost solutions:

Pneumonia - warm clothes, good nutrition, ventilation
Diarrhea - Clean water, sanitation
Malaria - Insecticide-treated bed nets
Measles - $1 vaccine
Neonatal complications - Breastfeeding, immunizations, skilled birth attendants

And most of the child-deaths happen in Africa:
SubSaharan Africa - 4.5 million
South Asia - 3 million
East Asia/South Pacific - 800,000
Latin America and Caribbean - 300,000
Elsewhere - 200,000

During humanitarian emergencies (Chile, Haiti, Darfur, Congo), children are the first to suffer. Be sure to help however you can by giving to your favorite charitable organization.