Safety device used in combination with child seat assembly

A safety device (6) used in combination with a child seat assembly (5) is provided to solve the problems about complicated structure and risk for the children. The safety device (6) includes a bracket (61), a first wing (62) and a second wing (63) pivotally connected to the head portion of the bracket (61), a flexible piece (65) cooperating the first and second wings (62, 63), a locking piece (64) releasably engaged with the first and second wings (62, 63). When one of the wings (62, 63) is pivotally rotated, both of the wings (62, 63) will be synchronously rotated to a vertical or horizontal state.