"What are they playing?"
Translation:वे क्या खेल रहे हैं?
The khelti is a verb which is used for girls, and is in past tense... Whereas khel is "normally" in present tense and, is used in almost everyone, they, we, she, he, you and me... All that change is the rahe which is written after the khel. E.g-> She is playing - Vah khel rahi Hai..., He is playing - Vah khel raha hai