Wait until your baby sits independently and holds their head strong, usually...

https://www.golf-bookmarks.win/most-experts-recommend-waiting-until-your-baby-reaches-9-to-12-months-your

Wait until your baby sits independently and holds their head strong, usually around age one. Start with a stable trailer for younger infants, then graduate to front or rear seats as they grow. Always fit a helmet correctly and ride safely together.