Serhiy Lysak, writing on the Telegram messaging app, said three of the children were in serious condition.
Reports on social media said a Russian missile caused the explosion and that an emergency services building was also hit.
President Volodymyr Zelenskiy, also writing on Telegram, said the explosion occurred between two dwellings.
"Unfortunately, there are people under the rubble," Zelenskiy wrote.
Pictures posted on social media showed rescue teams working at a shattered, smouldering building amid piles of twisted building materials.
Persons:
Serhiy Lysak, Lysak, Volodymyr Zelenskiy, Zelenskiy, Ron Popeski, Daniel Wallis
Organizations:
Press, State Emergency Service of, REUTERS, Saturday, Media, Thomson
Locations:
Russian, Ukraine, Dnipro city, State Emergency Service of Ukraine, Handout, Ukrainian, Dnipro, Russia