According to IATA (International Air Transport Association), Nicaragua has adjusted the entry requirements for yellow fever for children (see below). 
Yellow fever vaccination is mandatory for entry from the following countries (not for airport transit there): Angola, Argentina, Benin, Bolivia, Brazil, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, Colombia, Congo, Côte d'Ivoire, Ecuador, Equatorial Guinea, Ethiopia, Franz. Guyana, Gabon, Gambia, Ghana, Guinea, Guinea Bissau, Guyana, Kenya, Liberia, Mali, Mauritania, Niger, Nigeria, Panama, Paraguay, Peru, Rwanda, Senegal, Sierra Leone, Sudan, South Sudan, Togo, Trinidad and Tobago, Uganda and Venezuela.
Exempt from this entry requirement are: Persons >60 years old and children <9 months old.