Which episode does Coco meat a 1,000,000 screaming little girls?

I remember seeing on TV once a commercial for the show where Coco goes to somewhere (an elementary school, I assume), a door opens, & about 20 or 30 little bitty girls come running through it screaming excitedly (& that was seemingly before they saw Coco). I'm wanting to watch that episode on hulu or something, so it help if I know which one it is.
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