My son is receiving child benefits from social security. Does he file his own 1040, or does his SS income get filed with my spouse and me?

You do not include your son's social security benefit on your tax return.  If the social security benefit is the only income he received during the tax year, he is not required to file his own taxes.  

If he is claimed as a dependent and received income other than his social security during the year, he is required to file his own taxes if meets the following requirements :

https://ttlc.intuit.com/replies/3302185

Thank you for the detailed response.

You are very welcome !