Real Housewives of Orange County star TAMRA BARNEY is in for the fight of her life – to keep her children!

The reality star’s ex-husband, Simon Barney, filed court papers in Orange County, Calif., on March 28, accusing Tamra of being a horrible mom to their three kids – Sidney, 15, Spencer, 13, and Sophia, 8.

And he’s asking for FULL physical custody.

In the shocking documents, obtained exclusively by The ENQUIRER, Simon claims that Tamra’s neglect has “resulted in the children not getting prompt medical care, nutritional meals, hygienic care, and deterioration in their schoolwork and attendance.”

Simon also detailed a March 7 incident in which the couple’s son, Spencer, injured his thumb while in Tamra’s care.

“Although he complained it hurt, [Tamra] did not take him to a doctor,” Simon claimed.

Simon further stated that Tamra, 46, still failed to take Spencer to the doctor even after Simon specifically asked that she do so. He noted that Spencer’s thumb was “later found to be broken,” requiring him to take the boy to see an orthopedic specialist.

Additionally, Simon claimed that their youngest daughter, Sophia, often goes days without bathing, and that Tamra forges her schoolwork.

THIS isn’t the first the “RHOC” star and Simon have been at legal loggerheads. In December, Tamra asked an Orange County judge to overrule her ex and allow their children to be filmed for the ninth season of the Bravo reality show, which premiered April 14.

Simon contended that their older child had experienced “social ridicule” after scenes depicting their mom with strippers, sex toys and making crude sexual comments aired during the show’s last season.

According to a source, Simon only went after full custody AFTER Tamra attempted to get a court order allowing the chil­dren to be in the show, even after a psychologist recommended against it.

“Simon came to the realization that their kids would be better off with him full time than with their mother,” the source said.

This isn’t the first time Tamra has faced a custody dispute.

Last July, it was reported that nearly 20 years ago, Tamra dumped her oldest son, Ryan, who was just 9 at the time, on the doorstep of her first husband, Darren Vieth, a charge Tamra denied. Darren had sole custody of Ryan for “several years,” but says he gave custody to Tamra after her relation­ship with Simon got serious. “I’m still friendly with Simon to this day and will always be indebted to him for taking care of Ryan,” Darren said.

INCREDIBLY, Tamra’S BRAVO bio says that she and her third hubby – Eddie Judge, whom she married last summer – are considering having a child together, either by adoption or via a surrogate.

“Maybe Tamra’s fifth child will be the charm,” the source added, “since it appears she hasn’t done the greatest job in raising her other kids – at least according to her exes.”