Solaria

Solaria is the first child of Revelian and Luna. It was revealed that Luna was pregnant with her during the end of Jealousy: Love Triangle, meaning that the was concieved some time before Corruption: He Comes.

Solaria is born during Wrapping Things Up, where she is then kidnapped by Celestia. Solaria is later saved by Pinkie Pie, who actually ends up giving the suggestion for her name that they go with.

During most of the stories that she appears in, she is usually only brought up and involves problems that Revelian and Luna have with needing someone to babysit her while they're off saving the world. This leads to some important scenes during The Dark Emissary: Uprising involving Kuipter and Celestia.

When Solaria turned nine years old, she died, leading towards a bad time in Revelian and Luna's relationship which is elaborated during The Descent.