If he did not have any federal income tax liability in 2020, he should claim exemption from withholding on his Form W4. This will avoid the need to file a tax return just for purposes of getting a refund of any income tax
As a (your) dependent, filing Single and making less than $6000 this year, he will not owe any income tax - his personal standard deduction of $12,400 far exceeds his anticipated earnings.
From the IRS instructions on Form W-4:
Exemption from withholding. You may claim exemption from withholding for 2021 if you meet both of the following conditions: you had no federal income tax liability in 2020 and you expect to have no federal income tax liability in 2021. You had no federal income tax liability in 2020 if (1) your total tax on line 24 on your 2020 Form 1040 or 1040-SR is zero (or less than the sum of lines 27, 28, 29, and 30), or (2) you were not required to file a return because your income was below the filing threshold for your correct filing status. If you claim exemption, you will have no income tax withheld from your paycheck and may owe taxes and penalties when you file your 2021 tax return. To claim exemption from withholding, certify that you meet both of the conditions above by writing “Exempt” on Form W-4 in the space below Step 4(c). Then, complete Steps 1(a), 1(b), and 5. Do not complete any other steps. You will need to submit a new Form W-4 by February 15, 2022.
