This is the 2979th most frequent Russian word.
детском
The word "детском" is the prepositional case form of "детский," meaning "children's" or "child's" in English.
In this sentence, 'детском' is used as an adjective describing the noun 'park', indicating that the park is suitable or intended for children.
Ребёнок играет в детском парке.
The child is playing in the children's park.
Here, 'детском' is part of the adjective 'детский', referring to 'сад'. It means that the kindergarten is meant for children as part of its primary purpose.
Учёба в детском саду помогает развивать навыки.
Studying in kindergarten helps develop skills.
In this example, 'детском' is used to describe the noun 'возрасте', signifying it relates to the period of life associated with being a child.