The girls, ages nine to 10, wore silver paint and were dressed as wind goddesses blowing air into the sails of ships floating across a silver "lake" at the event, which was organized for participants of the St. Petersburg International Economic Forum.
Kirov Governor Nikita Belykh published a photo of the girls on Twitter, writing "In St. Petersburg, this is how they torture children. … Where is @Rfdeti?" referring to the Twitter account of Russia's children's rights ombudsman, Pavel Astakhov.
Some guests were outraged that the kids were left as part of the art exhibit.
"This creates a horrendous impression. I have no idea what this lordly entertainment is for," veteran rights activist Svetlana Gannushkina told Interfax.
Katya Solntseva of ABBYY software said she pulled the girls out after seeing them.
"The whole horror is not visible in the picture. The sun shone directly into the eyes of one girl. I think she stood so for at least an hour. I hope very much that her eyes were not injured. Especially shocking is that passersby were outraged, but took pictures and moved on. … Frankly, I really hope the organizers are punished," she wrote on the Facebook of influential blogger Rustem Adagamov.
The St. Petersburg governor's office denied any responsibility for the treatment of the children, saying the event was organized by a third party that had won a tender process for the event.
"The city only gave the financing. The responsibility lies with the victor in the tender," spokesman Andrei Kibitov told Interfax.