By Agence France-Presse
The accident happened in Cirebon, about 220 kilometres (135 miles) east of Jakarta.
The wall of warehouse next door fell over and crushed the local art centre where the junior high school students were preparing for a show.
Seven were killed as the building caved in, including six boys between 13 and 15 years-old and the centre's 48-year-old manager, police said.
Two 13-year-old girls were also injured, with one in a critical condition, they added.
Police are investigating the cause of the collapse, but they said initial suspicion has fallen on the age of the art centre which had been operating since around the 1940s.
"The building is very old, but we still need to ask experts to determine the cause of the collapse," local police spokesman Trunoyudo Wisnu Andiko told AFP.
Lax construction standards have raised widespread concerns about building safety in Indonesia.
In January, at least 75 people were injured when a mezzanine floor at Indonesia's stock exchange building in Jakarta collapsed into the lobby.
In February, the government temporarily halted all elevated transportation projects in Indonesia, after a dozen major accidents killed five and injured dozens more.