On June 28, 2010, the Administration published the interim final regulations prohibiting new group health plans and health insurance issuers in both the group and individual markets from imposing pre-existing condition exclusions on children under 19 for the first plan year (in the individual market, policy year) beginning on or after September 23, 2010.   These regulations apply to grandfathered group health plans and group health insurance coverage but do not apply to grandfathered individual health insurance coverage that was in existence on March 23, 2010.

Accordingly, for non-grandfathered individual health insurance policies, children under 19 cannot be denied coverage because of a pre-existing condition for policy years beginning on or after September 23, 2010. 

Click the following link to read the Q&A for clarification:

http://www.hhs.gov/ociio/regulations/children19/factsheet.html