Wait until your baby sits steadily with strong neck control, usually around 9...

https://devinmqjy235.iamarrows.com/what-weight-limit-matters-more-the-child-seat-or-the-rear-rack

Wait until your baby sits steadily with strong neck control, usually around 9 to 12 months. Choose a front mount for interaction, a rear seat for stability, or a trailer for cozy naps. Always fit their helmet perfectly before every ride.