By bicycle
Small
babies cannot be transported in bicycle seats, you have to wait untill their
backs are strong enough, this is at about 9 months of age by rule of thumb.
This contraption was made to overcome this problem, it is for rent and sale at Babyrent
Seats, for instance by Babyrent
A larger child, that can sit properly, can sit in the front or back seat, for instance a Bobike seat. Shop around, different bicycle stores have different prices for the same seats!