Usually, the IRS is rather prompt in asking for additional money. You can contact the IRS by calling 800-829-1040 (Monday–Friday, 7:00 a.m.–7:00 p.m. your local time). When calling, have a copy of your return on hand because you’ll likely be asked questions about your entries (e.g., adjusted gross income; taxable income; tax due) to verify who you are.
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.