Someone just asked a similar question so I'll give you a similar list I gave her. These organizations offer volunteer work with kids in Central and South America. Some lists are individual orphanages while others are large NGOs.
Casa Guatemala - An orphanage in Guatemala which offers volunteer work with kids (all 250 of them) at their orphanage.
King's Children's Home
- A private, non-profit organization that is dedicated to helping and providing
residential care for children in difficult circumstances regardless of their
social status, culture, race or religious belief. Offers cheap volunteer work with kids.
Genesis Voluntary Teaching
Program - Seeking volunteers to teach English to children in Ecuador
coast.
Casa Alianza - A nonprofit serving
homeless children and youth in Central America. Offers volunteer work with kids.
Nuestros Pequeños Hermanos
- Cares for orphaned and abandoned children in Latin America and the Caribbean
since 1954. Works in Mexico, Honduras, Haiti, Nicaragua, Guatemala, El Salvador,
Dominican, Peru, and Bolivia. Offers volunteer work with kids.