Claim it on your return, since it's only interest.
If his/her only income is from interest and dividends, Alaska PFD or capital gains distributions shown on a 1099-DIV, there is a provision for entering it on your return, using form 8814. Enter at Less common income / Child's income.
Using Form 8814 may even benefit a few parents who are not getting the full Child Tax Credit, as the credit will offset the total tax amount, including the child’s portion of the tax.
But, it may be best for him to file a separate return, if he has qualified dividends and capital gain distributions which could be taxed at a higher rate on the parent's return.
