Worth a look: Sky Crawlers
The story is of a young pilot who arrives at his new area to take charge of a new plane. He asks about the previous pilot, but gets little information. He is one of the kildren.
"Kildren can't grow up, right?" A character asks.
"It's not that we can't, it's just that we don't."
They do, however, reach puberty, and one of them, at least, has a child.
It's all a bit mysterious, at least if you haven't read the novels, but the mystery is what makes it interesting. The kildren use their planes in dogfights for what seems to be a pointless war in which, if one side is winning too much something will be changed to make them lose. Is the war just for entertainment? Is it just there to give the civilians a sense of threat that will enhance their lives?
The kildren can be killed. In fact, they die so often that they don't usually live long enough to notice certain things or begin asking questions about why their team mates die but come back with some, but not all, of their habits and memories intact.
The look of this anime is a little different from others. The backgrounds are richly textured and look like a computer game. There is, in fact, also a computer game based on this series.The characters are like cartoons drawn with a very fine pen that even gives detail to the eyes, which are not the usual large, limpid pools of most anime.
The strange kildren reminded me, of all things, of the sad clones in Katsuo Ishiguro's beautiful novel, Never Let Me Go.
Sky Crawlers is worth a look.