Police said the break-in happened Wednesday shortly after 3 a.m. in a neighborhood in the area of Church Street and East Colton Avenue.
The suspect is accused of getting into the home through an unlocked window.
"Once inside the house, the man touched a sleeping 10-year-old boy in an inappropriate manner over his clothing. When the victim woke up, the intruder fled through the window," Redlands police said.
The suspect is described as a white man with short, dark-colored hair. Police said he was wearing a black jacket and a "hospital-style" mask.
Anyone with information on the case or the identity of the suspect can contact Detective Truong at (909) 798-7681 or by email at firstname.lastname@example.org.