The Russian/Soviet size 1 Маска Детский 1А (МД-1А) was the small size mask included with the Противогаз Детский Фильтрующий Дошкольный (ПДФ-Д) kit.  It was made of gray rubber and sized for small children.  This example was made in Ohrenburg in 1976.

Маска Детский 1А (МД-1А) = "Child's Mask 1A (MD-1A)"

Противогаз Детский Фильтрующий = "Child's Filtering Gas Mask"

Дошкольный = "Preschool"

Similar masks in my collection:  Russian MD-1A size 4, Russian MD-1A size 5, Russian MD-3