small family; nuclear family
Refers to a small family unit, typically a nuclear family, as opposed to an extended family. Often used in sociological or demographic contexts.
In modern Japan, small families are increasing.
核家族 specifically means 'nuclear family' (parents and children), while 小家族 is a broader term for a small family unit.
shrinking family size; trend toward smaller families
Compound of 小 (small) and 家族 (family). The term is a straightforward combination of its components.