*Rich Homie Quan is at the center of an investigation from Georgia authorities after the rapper posed a video of himself puffing on…something, while his 1-year-old son sat on his lap.

According to TMZ, Child Protective Services and the Fulton County Police Department have now teamed up to investigate.

Our sources say CPS wants to sit down with Quan and ask a slew of questions … notably, what was he smoking? They also want to know if this was a one-off or his standard operating procedure.

Law enforcement tells us the probe goes beyond RHQ’s fitness as a parent … he could face possible criminal charges, including endangering a child and reckless behavior.