No, you cannot claim your son's capital gains on your tax return, unfortunately. A capital loss from selling assets in a custodial account cannot be reported on the parents' tax return. Parents can report the income of a child on their tax return in certain situations, but this option is available only when all the child's income is from interest and dividends. Since your child has capital gains or losses, all the child's income (including interest and dividends if he has any) must be reported on a separate tax return for the child and that includes, of course, his capital loss.