The period between ages 2½ and 4 is when children learn to make more adult-like sentences, complete with all the "little words." Sentence Jigsaw was designed expressly to help children make complete sentences. Around age 4, children have usually been able to use all the constituent parts of sentences (subjects, verbs, and objects) for some time, but they can still have fun inventing sentences while playing the game.
Sentence Jigsaw is based on an accepted principle of language acquisition: children learn the rules of language through repeated exposure to a range of examples. So, a child who frequently hears "The cat is watering the flower," will learn the sentence by rote. But if the same child also hears other sentences—"The cat is watering the apple. The cat is eating a flower." etc.—they will unconsciously understand that sentences are formed of a subject, a verb, and an object. In essence, children learn how to form simple sentences, and can then produce new ones by following the same structure.
Sentence Jigsaw also builds on children’s growing cognitive abilities. Around age 3, or even earlier, children enjoy laughing at absurd situations, like a cat watering a cookie, or a baby throwing a piece of cake. Additionally, children must build a puzzle to form the game board, which develops complementary cognitive abilities and fine motor skills.