The child was flown to Nemours Alfred I. duPont Hospital for Children in New Castle, Delaware, and the adult was taken to Shock Trauma.
CBS Baltimore reports at least 25 people were injured following an accident involving an overturned charter bus on southbound I-95 in Harford County.
Maryland State Police said there were 26 children, three chaperones and a driver on the bus.
Northbound I-95 between exits 89 and 93 will remain closed until further notice, authorities said.
"For reasons unknown at this time, the driver lost control of the vehicle, ran off the left side of the interstate, then back across all lanes of the interstate, hitting the front of the bus as it traveled across the roadway", said Shipley. A passenger auto may have been involved.
School Superintendent Dr. William Hite is holding a press conference at 2 p.m.at District headquarters to talk about accident.
Havre de Grace Police have blocked access to southbound I-95 via the ramp from Route 155, and traffic is crawling in both directions on Route 155 - which leads from the interstate to USA 40 in Havre de Grace. Two children were taken from a Maryland hospital to Children's Hospital of Philadelphia. On the other buses were police cadets who helped first responders get patients off the bus and get help, according to fire officials.
The bus was operated by charter company Werner Coach, according to a company spokesman.
Photos and aerial video from the scene showed the bus on its side, on top of a guardrail, with debris scattered across the road. The company says two critically injured patients were flown to hospitals.
At least two other buses and other cars are stopped near the overturned long, white bus with no apparent markings.