TELL THE KID THEY'RE NOT THE REAL THING!!
Classics Illustrated comics were not permitted in the house when I was growing up, so I started reading the real thing rather young, but I was raised speaking English by literate parents.
However, when my son was 1 to about 7.5 we lived in Thailand with my then-wife's family. He was fluent in Thai and Kammuang/Lao, and his understanding of Chinese was pretty good. His English was next to non-existent. When we returned to the States already knew the alphabet and he picked up spoken English rapidly, but had little western cultural background. I bought a case of
Classics Illustrated, so he could quickly get a grasp of stories, characters, etcetera essential to cultural literacy. My mother was not delighted with my strategy, but at least she understood and did not object.
Yes, I did tell him that the comics were not the real thing, and I told him why I got them for him. I let him enjoy them – then move on.