"Equipment" is the word used most commonly in American English to describe the apparatus used by children at a playground.
From Wikipedia, for instance:
"Modern playgrounds often have recreational equipment such as the seesaw, merry-go-round, swingset, slide, jungle gym, chin-up bars, sandbox, spring rider, trapeze rings, playhouses, and mazes, many of which help children develop physical coordination, strength, and flexibility, as well as providing recreation and enjoyment and supporting social and emotional development. Common in modern playgrounds are play structures that link many different pieces of equipment.
"Public playground equipment refers to equipment intended for use in the play areas of parks, schools, childcare facilities, institutions, multiple family dwellings, restaurants, resorts, and recreational developments, and other areas of public use."
Even very young children should become familiar with the word equipment.