That actually means that the cheese eats your child. 은/는 and 이/가 mark the subject and/or topic of the sentence and 을/를 marks the object of the sentence. In other words, xx는 eats xx를.
저 아이 means "that child (over there)."
In this case 저 is the same as is used in 저쪽, 저기, 저편.
To make it "my child" all you have to do is change it to 저의 아이 or 제 아이. In this case 저 means I or me, 의 means from/of (possessive), so 저의 literally means "my."
저의 = 제 (my) > 제 아이 = my child
저 (저기) = over there > 저 아이 = that child (over there)