Kim Zolciak has been making in-person visits to her son, Kroy "KJ" Biermann Jr., following his recent arrest for alleged aggravated sodomy and aggravated sexual battery ... TMZ has learned.

Sources familiar with the situation tell TMZ ... Kim has visited KJ multiple times since he was taken into custody. We're told Kim’s most recent visit was Tuesday with her daughter, Brielle Biermann.

As TMZ reported ... KJ remains behind bars following his August 17 arrest over allegations made by a teenage female classmate. Sources tell us KJ is doing the best he can while he remains behind bars.

According to court docs obtained by TMZ ... the girl alleges KJ forced her mouth onto his penis and digitally penetrated her vagina. The report says she was examined at a hospital, but doctors found no male DNA.

Kim has vehemently denied the allegations, previously telling TMZ ... KJ "categorically denies" ever engaging with the woman or the alleged conduct. She claims he voluntarily took and passed a polygraph exam and points to police records stating no male DNA was found.

Kim also claims the woman made similar allegations against two other people, though that claim has not been independently verified. She says false accusations can have "devastating consequences" but believes KJ will be cleared if the case goes to trial.