So, I'm just guessing here, but I'll bet the reason my game crashed is that I had my one teen girl jump on the family pony, to ride to the trading post to go shopping... just as (let's call it her aunt) was about to give birth. I hadn't really expected the aunt to be going into labor quite that soon, and so in the hullaballoo surrounding the new arrival, I sort of forgot about the departing niece. And so, just as the baby naming dialog was popping up, Thunder the Horse left the lot with his rider, bringing up the community lot. This loaded just fine, and the teenaged niece immediately started to make a beeline for the banquet table, but... being now more interested in naming the baby, I ordered her back to her horse, and sent her home... which caused the crash: When the lot began to load, the family portrait showed up just fine (with the wrong mother holding the baby - is that significant?)... and then, as the lot finished loading, BANG, it quit.
P.S. - I copied the last crash report to a text file, in case that's useful.

When reloading the game: in the Neighborhood view, all members are present, with the infant listed simply as "Baby Girl ____", but the family lot will now quit every time, upon loading. Had I backed anything up beforehand? No, of course not. As the rule usually goes, if a lot crashes once, it will always crash afterwards unless drastic measures are taken, only... I don't know what those measures should be.

Could I package the family members, somehow, bulldoze the lot, rebuild, and simply re-import them into CAS as a new family? The lot is fairly bare-bones, mostly outdoors, with lodges for the three individual families, so I could probably rebuild it in a couple of hours, I suppose... but would that help matters? Is the error on the lot, or within the Sims themselves? And if it's the latter, could I get away with exporting everyone BUT the unnamed kid, and picking up from there... or would there be destructive leftover memories of the birth? The infrastructure of the game is a bit murky to me, so I'm in unfamiliar territory here. I'm assuming that since the community lot loaded correctly, IT at least is safe, but I could be wrong, I guess. How to proceed?

I would first try just moving them out and back in again. The only safe way to export sims is to extract their looks in SimPE and make clones in a new neighborhood that you assign the right stats etc. to, but that probably isn't necessary. Babies sometimes show up being held by random people in the family portrait, it doesn't mean anything.

Thanks, that worked perfectly. Only thing is, the baby is still unnamed; not sure how to fix that one. Also, people keep handing her off to each other, like she's a football or something. Do the real parents not know she's theirs maybe? Right now I'm concentrating on re-buying all the stuff they had to sell when they moved out, but eventually I'd like to address this. Any ideas about that one?

Anyhow, thank you for the tip!

Make a backup of your game and run hood checker as a first step. See if the family loads. This may be enough to fix them.

If not, move the family out and try and load them on a blank lot. If yes great. You will know the error is not with them.

Then go and try and load their old lot, does it load? If the family loads and their old lot doesn't you can try and clean the lot or if you feel its easy to remake, bulldoze it and remake it and move them back in.

If their old lot loads but the family doesn't load then the error is with one of the sims. What I would try then is opening SimPE and deleting lines from each sim's inventory. May sound strange but I have made two crashing sims loadable again by doing that.

You can change anyone's name with the Sim Blender. Can the sims interact with the baby normally?