私は末っ子です。
tbd
I'm the baby of the family.
I'm the youngest in the family.
I'm the youngest child in the family.
は
1. indicates sentence topic
2. indicates contrast with another option (stated or unstated)
3. adds emphasis
指示句子的主题;表示与另一选项(无论是否明确提及)形成对比;表示强调