Kim Zolciak says she's witnessed her estranged husband, Kroy Biermann, smoke pot -- and she's afraid for her kids' safety -- asking a judge to step in and force him to get a drug test.
According to legal docs, obtained by TMZ, Zolciak says she's got serious concerns for the safety and well-being of her 4 minor kids while in Kroy's care ... and she points to his marijuana smoking as the source of her fear.
Zolciak is asking the judge to force Kroy to submit to a five-panel hair follicle drug screen .