"남자가 왼쪽에 있고 여자아이가 오른쪽에 있어요."
Translation:The man is on the left and the girl is on the right.
I don't have a mnemonic per se, but it's always helped me to remember the etymology of the words, and the fact that people have been biased against left-handedness forever: 오른 is from 옳다, meaning "to be right, true, proper" (good); 왼 from 외다, meaning "to be wrongly oriented" (bad) -- think 외국인, 'foreigner', those people from the "bad/left" side of the world.
That's true, (like 시외 버스 is the intercity bus because it travels 'outside' the city) but I was trying to draw a semantic connection between the words. While 왼 is of native Korean origin and 외 (外) is Sino-Korean, I believe they influenced each other at some point for symbolic resonance, since foreigners are historically 'outside' of what is normal in Korea like being left-handed and associated with a left-hand path is 'outside' of what is normal all over the world.
the conjunction article, "고" that is attached to the first verb in the sentence, "있고" is the conjunctive verb phrase that hinges the sentence together, properly translated as "and". It is a contraction of "있어요 허고" but saying it that way does not flow fluently, thus, the contraction.
It isn't that strict in real-life Korean, believe me. In fact, I have an example I can give to prove your point wrong. In the lyrics of PSY's well-known hit Gangnam Style, in the first verse, he talks about the girl she wants/his girlfriend and the word he uses for that is 여자:
낮에는 따사로운 인간적인 여자/ 커피 한 잔의 여유를 하는 품격 있는 여자/ 밤이 오면 심장이 뜨거워지는 여자/ 그런 반전 있는 여자
Also in the word girlfriend, 여자친구, 여자 is used, not 여자아이.
Koreans don't seem to care that much about being a virgin ¯_(ツ)_/¯