Older or Oldest ?

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~

the second oldest child

The second oldest child, because older mean bigger than.

the second oldest/ eldest child.
eldest cannot be used on non-human.

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

Wish it helps

第一個小朋友係the oldest child
第二個就應該係The second oldest child
唔係就唔多合意思

you can say ' The second child' instead of ' The second older/oldest child.

The second oldest child