Walking in Parc de Monceau in November,
I encountered a group of 15 to 20 children on a park outing with their teachers. 
Based on the ages (under 6 years), I guessed an école maternelle

Each child was wearing a bright yellow vest with reflective stripes,
and from a distance they looked like a little swarm of bees darting about.

Parc de Monceau
Rue des Courcelles
75008 Paris