Telescopic backrest and child safety seat

The utility model belongs to the technical field of child seats, and provides a telescopic backrest and a child safety seat, the telescopic backrest comprises a seat back, the seat back is provided with an accommodating cavity, locking grooves are uniformly distributed in the accommodating cavity along the vertical direction, and the locking grooves are communicated with the accommodating cavity; the headrest is connected into the containing cavity in a sliding mode, a moving block capable of moving in the length direction of the headrest and a locking block forming an included angle with the moving block are connected to the headrest, a traction groove is formed in the moving block in the thickness direction of the moving block, the traction groove and the moving block are arranged to form an oblique angle, and the locking block is movably inserted into the locking groove; and one end, far away from the locking groove, of the locking block is movably clamped in the traction groove. Compared with the prior ar