The toys are shaped like grenades and contain two powders that react when they are hit or stepped on, setting off an explosion like that of a firecracker, Tuoi Tre News reported. The reaction also produces a strong smell.
At least 37 students at Chu Van An Primary School in Dak Nong province were sickened last week after playing with the toys, a doctor at Dak Nong General Hospital said. Seven were re-hospitalized Monday.
The symptoms included respiratory problems, chest pains, muscle contractions and blood in their stools, said Dr. Pham Thi Kim Hue of the hospital's pediatrics department.
The children told police they bought the toys at a shop near the school for 1,000 dong (5 cents) each.