How did my child get warts?

Common and plantar warts are contagious but not extremely so. A break in the skin is usually required for the virus to cause an infection. Infection with the wart virus does not always result in a wart, and the wart virus may be in the skin for years. It is therefore very difficult to determine where your child picked up the wart virus that caused a common or plantar wart.
Your child may catch the wart virus:

Habif TP. 2010. Clinical Dermatology: A Color Guide to Diagnosis and Therapy. 5th edition. Mosby Elevier. P 454-464.
Smolinski KN, Yan AC, 2005. How and When to Treat Molluscum Contagiosum and Warts in Children. Pediatric Annals 34:3:211-221.
What to Do About Warts. In: Harvard Women’s Health Watch. December 2004. p. 6-8.