I took my kids around in a bike trailer for the first seven or so years of their life. I didn't do this exclusively---we had a car and often used it, but the majority of places I wanted to get to I could reach by bike and bike journeys were 100% to 5% depending on the location. Now they are old enough to ride their own bikes. This was in the fairly bike unfriendly city of Birmingham, UK. (Birmingham bought into car culture in 1960s and is slowly recovering.)

Better to look at cities that are better adopters of bikes, such as Copenhagen. There just about everyone is on or in a bike, including many children. They love their cargo bikes over there. See https://triobike.com/ and http://denmark.dk/en/green-living/bicycle-culture/copenhagen...