Annualize/estimate his income and use TurboTax's W-4 withholdings calculator: https://turbotax.intuit.com/tax-tools/calculators/w4/
For 2023, if a minor makes more than $13,850 from working, they have to file taxes. The filing threshold for unearned income, like interest your child earns from a savings account, is $1,250 for 2023.
Dependent status is equally important to this equation. If you claim your child as a dependent, and they meet these income thresholds, they need to file a tax return. But, there's another option: If they only have unearned income, and it's less than $12,500, you can choose to include this income on your own tax return.
Be sure to indicate if you are claiming him as a dependent.
The filing threshold for 2024 is likely similar to 2023.