Why do you think you will not receive the third stimulus payment if you claim your son as a dependent?
IRS website for the third stimulus payment information - https://www.irs.gov/newsroom/more-details-about-the-third-round-of-economic-impact-payments
How much is the third Economic Impact Payment?
Those eligible will automatically receive an Economic Impact Payment of up to $1,400 for individuals or $2,800 for married couples, plus $1,400 for each dependent. Unlike EIP1 and EIP2, families will get a payment for all their dependents claimed on a tax return, not just their qualifying children under 17. Normally, a taxpayer will qualify for the full amount if they have an adjusted gross income of up to $75,000 for singles and married persons filing a separate return, up to $112,500 for heads of household and up to $150,000 for married couples filing joint returns and surviving spouses. Payment amounts are reduced for filers with incomes above those levels.
