children from a multiple birth
Refers to each child born from a multiple pregnancy (twins, triplets, etc.). Used in medical, statistical, or formal contexts.
The number of children born from multiple births is increasing year by year.
Raising children from a multiple birth is tough, but the joy is also great.
Refers to the pregnancy itself (multiple pregnancy), whereas 多胎児 refers to the resulting children.
Compound of 多胎 (multiple pregnancy) + 児 (child). The exact historical derivation is uncertain; the term is a modern medical coinage.