The most common malignant neoplasm of infancy is:

Neuroblastoma accounts for 7-10% of pediatric malignancies and is the most common solid neoplasm outside the CNS. Fifty percent of neuroblastomas are diagnosed before age 2 years and 90% before age 5 years. Ref: Kligman, Behrman, Jenson, Stanton (2008), Chapter 498, "Neuroblastoma", In the book, "Nelson's Textbook of Pediatrics", Volume 2, 18th Edition, New Delhi, Page 2137