nursery school sleepover
An overnight stay event at a nursery school or kindergarten, where children sleep at the facility as part of a group activity.
Next week, there will be a nursery school sleepover at the kindergarten.
At the nursery school sleepover, the children all slept together.
Variant spelling using 泊り; equally valid.
Compound of お泊まり (o-tomari, 'staying overnight', from 泊まる tomaru) + 保育 (hoiku, 'nursery care').