Wait until your baby sits unassisted and holds their head steady, usually...

https://www.first-bookmarkings.win/wait-until-your-baby-sits-independently-and-holds-their-head-up-steady-while

Wait until your baby sits unassisted and holds their head steady, usually around nine to twelve months. Always prioritize neck strength over age. Before your first trip, ensure a toddler helmet fits snugly