The first robbery occurred in the 1100-block of North State Street at 3 p.m. on January 8 and the other robbery occurred in the 100-block of North State Street at 1:40 p.m. on January 10, police said.
Police said the thieves showed or claimed to have a gun before taking money from the juvenile victims.
One of the robbers was described by police as having a tattoo of a cross on his forehead.
Anyone with information is asked to contact Area Central detectives at (312) 747-8380.