Children’s Streets” consist in pedestrianizing the streets around nursery and elementary school. The aim is to make the route between home and school safer for children, but also to combat pollution.
Removable barriers are installed wherever possible. They allow the passage of emergency vehicles and services (garbage trucks, etc.), but prohibit the passage of other motorized vehicles.
More picture and before/after sliders at the bottom: https://www.paris.fr/pages/57-nouvelles-rues-aux-ecoles-dans-paris-8197#des-rues-aux-enfants-avec-un-amenagement-specifique
It did, but the last time was in 1860. Maybe it was too busy after that (you know, 1870, 1914, 1939…)