末っ子を英語でなんと言うか？

そのほかの言い方はともかく、ここでは baby of the family をおぼえましょう。1:38 I'm the baby of the family. 私が姉妹の末っ子です。

Th Girl Who NEVER AGES - Extraordinary People Documentary - Frozen in Time

https://www.youtube.com/watch?v=0jkFsGaZ1Js  0:37 my sister Monica is the baby of us, of the seven. モニカは七人兄弟の末っ子です。
This Woman Is Desperate To Find Her Baby Sister | Long Lost Family

練習問題解答
a-4885 the baby of the family
a-6814 the baby of the clan