Here's why:
* Subject: "The children"
* Verb: "are"
* Present Participle: "jumping" (used as an adjective describing the children)
* Object: "in first grade"
Even though "jumping" is a present participle, the main verb "are" is in the present tense, making the whole sentence present tense.
It's important to note that the sentence is grammatically correct, but it's not a typical sentence structure. The phrase "jumping rope" is a participial phrase functioning as an adjective, which can sometimes be considered a bit awkward. You could rephrase the sentence to be more direct, such as:
* "The children who are jumping rope are in first grade."
* "The first graders are jumping rope."