Ken and Chun li's kids were little in 3 and teenagers in 6.
The math just adds up there.
It would, if SF behaved like the real world.
It doesn't. SF operates on a sliding timeline. The same way comic books do. Ryu and Chun Li are not 50 for the same reason that Batman and Superman aren't 100. And why kids in comics grow up, but the adults don't get old.
The current SF game always takes place "now" with the other games in the series shifting around in relation to the current game.
For example: When SF3 first came it it was taking place in 1997. Because that was "now" at the time it came out. But when SF4 came out, it was taking place in 2009, because that was "now" when IT came out. But SF3 takes place AFTER SF4. Which means SF3 now takes place sometime AFTER 2009.
The most obvious example of this is SF5. Which still takes place before SF3. But a bunch of characters in that game have smart phones and messenger apps. If SF3 was still taking place when it was originally, SF5 would be someplace in the 90s, when those things didn't even exist.
The way the SF timeline is currently is:
SF6 is happening NOW
SF3 was "a few years ago"
SF5 is "a little before that"
SF4 is "a little before that"
SF2 is "a little before that"
SFAlpha is "a little before that"
SF1 is "a little before that"
The entire series takes place over, like, less than a decade. Even though the games have been coming out for 35+ years.
Castlevania did actually incorporate more of Bram Stoker's lore into its official story... later on. So it's not nearly as "its own thing" as being said. It's still its own thing, clearly, but it doesn't remix it that much either.
Not to mention, the Bram Stoker novel is literally part of the official Castlevania timeline. In 1897.