noun
nursery cooperation day
A day designated by a nursery school or daycare center when parents are asked to keep their children at home, often to reduce staffing needs or for special events.
来週の金曜日は保育協力日なので、子供を家で見る予定です。
Next Friday is a nursery cooperation day, so I plan to look after my child at home.
Compound of 保育 (childcare) + 協力 (cooperation) + 日 (day).