What's childish is expecting people to like it just because you do.
The manga is Sadamoto's project, and he can do with it what he likes. But I'm not obliged to like it if it doesn't speak to me on any level, and nor am I obliged to give it praise just because of its connection to the show. There are just too many "wtf?" moments throughout for me to give it a passing grade. Doesn't mean it didn't do anything right, because that's not so; I liked Kaji's background, I liked some of the general worldbuilding, I liked a bit of Shinji's snarkiness. But overall I feel like it stripped out most of NGE's primary themes even while trying to tell the same story, and that just doesn't work. The changes to Shinji and Asuka make this especially problematic.
If you don't see it you don't, but those of us who do aren't being childish about the matter as a result. We're just not impressed with what we've been given and have moved on to other things.