The gun was a stolen BB gun, and investigators are still working to determine its owner, the police said.
Police said the victim, identified only as a juvenile male, was approached by the three boys in the popular, 300-acre park off Oakland Mills Road. One of the boys had the gun and the victim gave up his backpack, according to police. No one was injured and the boys fled.
The youths were charged with armed robbery, robbery, assault and theft. Their names were not released and it could not be determined whether they are being held in a juvenile detention center or were released to parents or guardians.
“Juveniles are only charged as adults if the crimes meet specific criteria by state law,” Sherry Llewellyn, a police spokeswoman, said in an email.
Howard juvenile arrests are down 35 percent for the first half of 2018, when compared with the same six months last year, Llewellyn said.
In another high-profile case, three boys were charged in July with assault, burglary, motor vehicle theft, robbery, reckless endangerment and theft in what police called a “three-day crime spree.”
The boys — 11, 14 and 15 years old -- were accused of stealing a golf cart from Columbia Mall and attempting to steal a purse at the county’s Central Library.