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

https://www.fastbookmarks.win/start-biking-once-your-baby-sits-well-unsupported-and-holds-their-head-steady

Wait until your baby sits steadily with strong neck support, usually around twelve months. Front seats keep them close for interaction, rear racks offer better balance, and trailers provide comfort for naps. Always check for a snug helmet fit first.