Prosecutors said the couple's abuse of their son resulted in several hospital visits since October last year. His weight had dropped to just 13 kgs when he was admitted to Children's Hospital in Madison in April.
Barbara Knox, a physician and child abuse expert at Children's Hospital, told investigators that the boy had experienced the 'most egregious example of child starvation and torture' that she has seen, according to the criminal complaints.
Investigators said Kimberly grew angry at hospital staff when they gave her son food and told them she believed he was manipulating her and others to get a "vacation" at the hospital.
Knox said the boy's current medical condition puts him at "risk of great bodily harm and/or death."
The hospital said he was being monitored for a condition known as refeeding syndrome, which is sparked by severe malnutrition, and ordered that he be given unrestricted access to food.
The complaints say the parents described their son as "controlling, demanding and abnormal" in his refusal to eat and manipulate others.
The staff at Children's Hospital described the boy as "sweet, polite and very normal."
The Fahrenkrugs have claimed the helmet they made the boy wear protected him from banging his head and that the other gear helped him strengthen his legs.
They also denied withholding food from their son and claim he stopped eating.
The married couple faced Brown County Circuit Court via video link on Monday where they were charged with five felonies, including first-degree reckless injury, causing mental harm to a child, first-degree recklessly endangering safety, child neglect resulting in great bodily harm and false imprisonment.
Cash bond of $100,000 each has been ordered for the couple who are jailed in Green Bay.
