Under the PPACA, adult children may be covered under the parents health benefits plan (insurance) until age 26. The child does not have to be financially dependent on the parent, and can be married. Normally, such a situation would require that the value of these benefits be imputed income to the child. However, the IRS has made it clear that there is no imputed income when complying with this provision of PPACA.
That is not so with the various states that have an income tax. Some states will require imputed income; some may follow federal law and others such a New Jersey and New York have not made a decision at this point.
Individuals who have enrolled such children may receive a surprise at year-end when the child receives a tax statement with imputed income of several thousand dollars. The value of single coverage could easily be $5,000 to $6,000 and that would mean a tax bill based on the tax rate in their state.
You may want to seek clarification of how this will be handled in your state and by your employer if you are enrolled in a group health benefits plan.