The children were the Jefferson County man's 9- and 12-year-old sons and two neighbor kids, ages 13 and 15, according to court documents filed by prosecutors.
The 42-year-old man pleaded guilty Friday to four misdemeanor counts of endangering the welfare of a child. Prosecutors dropped felony charges that included making threats against public officials and others.
In keeping with the plea agreement, District Judge James B. Wheelis sentenced the man to 180 days in jail for each charge, all suspended. That amounts to two years of probation, minus the 80 days he has already spent in custody, the Independent Record reported.
The Associated Press is withholding the man's name because it doesn't identify minors who are victims of crime or abuse, and releasing the man's name would identify his sons.
The man was arrested in December at the Helena airport after returning on a flight from Alaska.
His girlfriend at the time said he broke her wrist and some fingers Dec. 5 when she tried to stop him from waterboarding his sons, court documents said. She said the man straddled each boy with his hands over the child's face and mouth, and dumped water on their faces to simulate drowning, the records said.
The woman told investigators that the man described it as a learning experience for the boys.
The two neighbor children told a Child Protective Services worker that the man also had waterboarded them, prosecutors said.
Prosecutors said in court records that a witness had reported that the man had body armor, assault rifles and armor-piercing ammunition.
Investigators found some ammunition and three rifles that may have belonged to the man. Authorities did not elaborate on what kinds of weapons specifically were found or suspected.
Jefferson County Attorney Mathew Johnson said the plea deal was reached after a thorough review of the evidence. The agreement calls for deferring prosecution of the man on a charge of partner or family member assault.