。
The dancers skipped lightly across the stage.
Literal
Dancers [topic-は] stage [object-を] cross-[and-て] lightly were-dancing-going.
横切る ('to cross / traverse') takes を, like 渡る ('cross') and other motion-across verbs. 軽々と is a reduplicated adverbial meaning 'lightly / easily / effortlessly' — the doubled form intensifies the sense of lightness. 踊っていく combines 踊る ('dance') + ていく (motion away).