Wait until your baby has strong head control and sits up on their own before...

https://www.parenting/when-can-a-baby-go-in-a-bike-seat-an-age-by-age-guide/

Wait until your baby has strong head control and sits up on their own before hitting the trail. Whether you are looking at a rear seat or a trailer, I have broken down what to watch for. Let’s ensure your little passenger is ready for the ride.