First you decide whether your report the child's investment income on your FEDERAL tax return or file a separate tax return for the child.
If his only income is from interest and dividends, 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. Otherwise, the child must file his own return, if he has sufficient income.
If you file the child's income on your return, Calif. also has a provision for filing it on your state return. See <a rel="nofollow" target="_blank" href="
https://www.ftb.ca.gov/individuals/FileRtn/7.shtml">https://www.ftb.ca.gov/individuals/FileRtn/7.sht...>,
If not, you will have to file separate state and federal returns, so your question may be academic.
I don't know if TurboTax can handle that (CA form FTB 3800), but I have flagged your question for the TT moderators.
