Following the explosion at 8pm on Saturday, three boys aged 15-16 were spotted running away and were swiftly caught by police, Pol Col Decha Phromsuwan, an investigator at Lumpini Police Station, said yesterday.
No one was wounded.
Police directed one boy to contact his four friends, leading to their arrests in the Sathu Pradit area.
The youths told police that their group of seven was riding a bus when three of them got off at a bus stop.
Thrown 'for fun'
One of those on the bus pulled out the ping-pong bombs assembled on the bus from materials bought from a Phu Khao Thong shop to throw them for fun before fleeing the scene.
Two boys were charged with possessing explosives without a permit and carrying them in a public place without sound reason.
One faced an additional charge of detonating a device that caused property damage.