Wait until your baby holds their head up and sits independently, usually by age...

https://smart-wiki.win/index.php/Can_a_Baby_Sleep_in_a_Bike_Seat%3F_A_Service_Writer%E2%80%99s_Guide_to_Safety_and_Comfort

Wait until your baby holds their head up and sits independently, usually by age one. Choose front seats for closeness, rear mounts for stability, or trailers for a cozy ride. Always ensure a perfect helmet fit and keep your first rides short.