FITCHBURG — The mother accused of assaulting her two young children was nowhere to be found when police found her beaten 6-year-old daughter unresponsive at home with her injured 9-year-old brother.Cops searched for about 2 1⁄2 hours for 37-year-old Shana Pedroso, pinging her cellphone five times to track her, according to a Fitchburg police call log from Tuesday.The police alert for Pedroso warned she “may be armed and dangerous,” the log said.