Wait until your baby can sit up steadily and hold their head up, usually around...

https://www.stealth-bookmark.win/most-babies-are-ready-for-bike-rides-once-they-sit-independently-and-hold-their

Wait until your baby can sit up steadily and hold their head up, usually around age one. Front seats allow easy interaction, while rear mounts grow with your child. Trailers provide extra stability for naps. Always choose a properly fitted helmet.