Wait until your child has strong neck control and sits independently, usually...

https://www./parenting/when-can-a-baby-go-in-a-bike-seat-an-age-by-age-guide/

Wait until your child has strong neck control and sits independently, usually around age one. Use a trailer for younger ones. Once they have core strength, pick a front seat for an interactive view or a rear seat for a stable, comfortable ride