Which comes first... fixing the attitude so young mothers feel safe or somehow convincing "road fulls" of young mothers that they will change the attitudes of others...

The fact is that where cyclists fill the streets... the "fix" was top down, and included strong government support for cyclists, training of future generations to have the right attitude, making cyclists feel welcome and safe on the streets and making motorists feel less welcome and more responsible for collisions with other road users... it took all that to make cycling what it is in "some" European countries.