、。
I knew about pseudo-myopia, but I really didn't think my own child would develop it.
Literal
Pseudo-myopia [called-というのは] knew [but-が], no-way own [genitive-の] child [subject-が] pseudo-myopia [into-に] become [such-thing-なんて] not-thought was.
A worried parent's lament. まさか ('no way,' 'you can't be serious,' 'surely not') is an adverb of incredulity that precedes a negative or surprising outcome — used to frame the main clause as something the speaker had dismissed as impossible. なんて ('something like,' 'such a thing as') is the dismissive topicalizer, carrying surprise or disbelief about the topicalized event. 仮性近視 ('pseudo-myopia,' 'temporary nearsightedness') is a medical compound for temporary blurry vision caused by eye muscle strain, often reversible — common in children who spend too much time reading or on screens. The frame ~と思ってませんでした (the negative past of ~と思う, with casual ~てません contraction) is 'I didn't think that X,' used when X turns out to be true after all.