AN explosion rocked central Oslo on Tuesday after cops detonated a grenade and arrested three children. An investigation is underway into the blasts in central Oslo, with police saying they believe multiple people were involved. Cops warned the public to stay away from their windows as there were likely to be more explosives. "Given that there is still an explosive device in the area, the police wish that people stay away from windows," it continued. Bislett - where the explosions occurred - is in central Oslo, as is a suburb popular with families.