A set of elements giving the possibility of forming two types of wheeled devices for children which comprises: a platform (10), a handle (3) comprising an upright (20) intended to be connected to the front of the platform (10), and a removable seat (6); said handle (3) is removable with respect to the platform (10), and the platform (10) comprises, on the side of the front wheel(s) (11), a well (13) for receiving the lower portion of the upright (20); the platform (10) comprises a front boss (14) and said well (13) opens at the upper portion of this boss (14); the set of elements comprises a body (4) for supporting the seat (6), the front portion (4a) of which has a front extension (22) and a rear extension (23) defining together a housing (24) having a recessed shape corresponding to the shape of the boss (14); the set of elements comprises means (28, 31) for mounting the seat (6) on said supporting body (4), and the set of elements comprises means (5) for attaching at least one of said extensions (22, 23) to the platform (10).