If all of your child's income was in the form of interest, dividends, and capital gain distributions (e.g., from mutual funds), and the amount is more than $950 but less than $9,500 for 2012 ($1,000 and $10,000 respectively, for 2013) you can elect to report the income on your own return rather than filing a separate return for the child.
The IRS allows you to treat your child's income as your own, ostensibly to save you time. For a child under 18, all unearned income above $1,900 (for 2012) must be taxed at the parent's rate, and including the income on your return forces you to calculate this amount.
However, the time you could actually save is minimal at best. If you decide to go this route, you must also complete a Form 8814 for each child and attach it to your tax return.
The file is in Adobe Portable Document Format (.pdf), and you will need the free Acrobat Reader to view and print the files.
Federal Income Tax Obligations