It depends on whether you itemized medical deductions for the year in which you pay the premiums on the policy you purchased on the individual market. If you took the standard deduction, you don’t report the payment. If you itemized, you report the payment as “other income” to the extent you received a tax benefit from it in the prior year. Similarly for those who are self-employed and deducted the premiums from gross income, the payment must be reported as “other income” in the year it’s received.
The tax on the investment income in excess of $1,700 (may change after 2007) of a child under age 18, based on the parents’ marginal tax rate and computed on Form 8615.