If the 1099-INT for your grandson is the only income that he received in 2024 and it was less than $1,300 in investment income (interest, dividends, and capital gains) then you aren't required to report this income. If the investment income is greater than $1,300, you must file a separate tax return for your grandson.
Review the TurboTax article Do I need to report my child's 1099-INT on my return? for additional information.
If your grandson's investment income exceeds $1,300, it should be reported on his parent's tax return unless he's your dependent.