it should be
"the second oldest child"
or juz "the second child"
其實同中文相似,
你會話"第二個最大嘅小孩"
如果你係想表達家中第二大嘅兒子,
簡簡單單話係"the second child" 就 ok 架喇~
you could say, " I m the second child in my family"
The second oldest must be wrong..because Oldest is Superlative words....If you put "second" in front of it...it contradicts the meaning of it the word " oldest".....
Usually people wont use oldest to express the 排行....but use eldest instead....
I m the eldest sister means 排行第1