Grouchy Imp said:
Let's bring up my favourite two from Fallout 3:
1) Vault 87. Computers in Vault 87 specifically mention the FEV virus wanting to "level the playing field" by converting both males and females into androgynous subjects, yet in Fallout 1 you defeat The Master by revealing to him that Super Mutants aren't a viable branch of human evolution as whilst the males retain the ability to breed, females are rendered sterile, leading The Master to pull the plug on his experiments and end the Super Mutant threat. A seemingly small change, but one that invalidates the ending of F1 and by extension invalidates the entirety of F2 as the Vault Dweller would not have survived to found the tribe living in Arroyo.
2) Little Lamplight. A community that has existed for the last 200 years in isolation despite ejecting citizens as soon as they reach puberty. If you need this explaining to you then I officially give up.
1. "Male" super mutants on the west coast never retained their ability to breed, what Marcus said in Fo2 about "taking a few years for the juices to start flowing again" was confirmed to be a joke, both "male" and "female" super mutants are 100% sterile in all Fallout games.
http://fallout.wikia.com/wiki/Marcus
"While Marcus says that he is no longer sterile, Chris Avellone, who wrote that dialogue, confirmed that Marcus was only joking and that super mutants remain entirely sterile. "
Also, the strain of FEV used in Vault 87 was different from the Mariposa strain, hence why the Vault 87 super mutants look and grow differently. It is but one of many FEV strains that has different effects, like FEV strain "Curling-13", made by the Enclave to kill all mutants, and Eden's modified strain of FEV, based off of the curling strain, which does the same thing, but via water instead of air.
2. LL ejects kids when they reach 16, its possible to have kids as young as 14. Also, LL is not isolationist, they are proven to take in orphaned kids, such as the case from the kid from Greyditch, they are known to frequently send people out to scavenge food, and their city is well known to the people of the wasteland, from Paradise Falls to Rivet city, and given the state of the wasteland, its far from improbable that parents wouldn't either leave their kids at LL because they either don't want them, or can't feed them themselves.