Explain, please. Why they shoudn't do it at all?
Little Lamplight is the main reason. Nothing about that place made any [censored] sense. It was populated entirely by children for 200 years (with no explanation on how the place managed to
maintain a population). It was not only the farthest place away from civilization in the entire game, but it was smack-dab in the heart of Super Mutant territory, literally on the doorstop of their base, and with signs that the mutants had even encroached on it. The dialogue of the kids was terribly written and absolutely annoying, and the game didn't have the decency of allowing you to even retort against the little punks as they insulted, demeaned, and threatened you. And in order to complete the main quest, you have to go through this nonsensical location, you can't even ignore it. And depending on your build, you might end up having to interrupt your progress just to do some meaningless side quest halfway across the map before they'll let you in (to rescue some friends from Paradise Falls). Bethesda also made the mistake of hiring child actors to voice them all, and none of them were particularly good.
Simply put, in Fallout 3, Bethesda [censored] up
hard when it came to children. They made the kids absolutely irritating, they shoved them in your face, and they were so [censored] horribly written and used that they hurt immersion more than they helped it. And pretty much sapped up any faith I had in them (which was very little, mind you) to ever do a decent job with children again.