Looks like after Lynn, the parents actually took a break in sex.

Leni and Lori are actually legal according the laws of my state (16 and older is actually what's legal in the majority of US states, but because California's one of the few states where it's 18 a lot of media made there just acts like the legal age is 18 throughout the whole country; one of the reasons I even know this is thanks to an episode of Archer where a 16 year old nympho tries to get with Archer the whole episode and he keeps trying to get her away from him, but I found out via TV Tropes that it turns out that in the real world she would have been considered legal by the laws of the country Archer and her were in in that episode, so that episode got me curious "so wait are there any other places where 16 is considered legal?" and to my surprise 16's considered legal in all of Canada and in more than 30+ US states).