Not only remember but him as a little child realised and was conscious of the whole situation(taeju even mention this in that scene saying he is scared)...
SSSSHHHHH SHHHHHH SHHHHH NO HE DOESN’T i scream as they drag me away to the padded room
They only remember selective fragments, and a lot of times those memories are kind of random, not necessarily related to strong emotions or anything, just random
Don't overthink it guyssss
You just reminded me of this
the fact that the kid remembers that memory even at one year old means that he also remembers the memory of when his older bro tried to KILL THEM BOTH bu drowning at the sea