What type of income does your child have?
If they had a job, then their income is calculated using the same tax bracket rates as everyone else based on their income.
If they have unearned income above $2,300, then they would be subject to the kiddie tax. This means, their unearned income over $2,300 would be taxed at the same rate as you.
If you walked through and were asked what your income was, then you would be filling out form 8615 for the kiddie tax.
If their ONLY income is interest and dividends and was less than $11,500, you can choose to report that income on your own return using form 8814 instead of filing a separate return for them. To do this, you will select Income>>Show More next to Less Common Income>>Start next to Childs Income. If they have other income, besides interest and dividends, you cannot report their income on your return.