Base assembly and child safety seat

The present disclosure discloses a base assembly including a base; a sliding element telescopically arranged on the base; a supporting leg which is pivotably connected to the sliding element and extended and retracted along with the sliding element, and which has an unfolded position when in use and a folded position when not in use; and a supporting leg retractable structure, which actuates the sliding element and the supporting leg to move toward inside of the base together in response to pivoting the supporting leg from the unfolded position to the folded position.