Yes, Japanese kids read American comics but only a few of them do maybe because of the following factors:
1. Language. Hardly, most (not all) American comics never get translated to Japanese, and most Japanese kids are not that adept in reading English, which is in contrast to Manga which is translated to English by media companies (and fans) and made available to readers.
2. Competition. In a usual Japanese comic book store you will see a plethora of Manga (even bible-thick ones), so if ever there will be an American Comic there it would be hardly noticed unless someone really sought to have a copy of it.
3. Culture. Japanese kids will likely to read Manga over American comics because they are much more accustomed to the style and art of Manga, as the latter is created or intended to be read by them. The "feel" of American comics is still something for them to be accustomed to.
But, some Japanese (young and old) read American comics. They admire it's art and story. You will notice that some Manga authors pay homage to their favorite American Hero or comics, (like Masakazu Katsura who inserts cameos of Batman in his manga). Some people in the comic and manga industry would say that Manga and American comics tend to influence each other. Just think that Osamu Tezuka, the one coined as "God of Manga" is influenced by American comics such as Betty Boop or Felix the cat. So, in conclusion, I would say, Japanese kids do read American comics, but not as much as American readers (or any foreign reader) do.
16 years of watching and reading anime and manga, respectively.