The three were family friends of the plane's owner, 45-year-old Jacek Mazurek, of Kearny. He was killed in the crash, as was the pilot, 46-year-old Wojciech G. Nykaza, of Lodi.
Police Capt. Timothy Clayton said the 6-year-old's parents were at the Monmouth Executive Airport when the plane went down, but that they did not witness the crash.
Officials say the twin-engine craft had completed a takeoff pattern from the airport before a piece of the plane fell on the runway and it crashed Monday. Debris was scattered over a 200-foot stretch.
National Transportation Safety Board investigator Jose Obregon says it's not clear whether the pilot was trying to land or the accident just happened.
"It's in a ball. The majority of the major fuselage and cabin area is there, but it's pretty twisted. The cockpit area and cabin area is very crushed. We're trying to get some information on the operator and the aircraft, but it takes a little bit to get a good understanding of the maintenance, the pilot and the aircraft's history," an NTSB spokesman said.