Most of this hasn't been exclusive to one save, as I'm a family player. Its infiltrating all of them.

The only thing that is exclusive to it is the crashing, which I don't think is related but could be as the flashing has gotten substantially worse, and after the babies were born so did the crashing.

I think the crashing is actually just fault of my horrible pc trying to run all of the packs at once with tons of mods.

However I know my computer doesn't cause the weird flashing.

I was looking through my screenshots for an image of the glitch and I did remember my sim had twins so that could explain why it got worse... but not why its happening in the first place.

I couldnt find any photo evidence of it actually happening but tomorrow I'll try to boot up the game and take a screenshot.

I can deal with just aging them up into toddlers and such if its unsolvable but it really feels like missing out on such an important part of their life yk?

Only thing I can think of, is if you are using some default baby replacement CC, or baby mod.

Oh!!! Yeah because at one point I had the floating hair glitch, and the boot glitch so I temporarily downloaded the defult hair and some random shoes that were invisible. I'll try to find the mod.

I found it and uninstalled it. So far I havent had any issues and I moved around a lot.

This mod is https://modthesims.info/download.php?t=591846

I don't think that its a bad mod, I just think I might have broken with a few other mods I have or something.

The game did crash, but again I think that is a different problem

I had this problem.
I downloaded some custom infant CC - specifically HAIR CC and it somehow fixed itself...
I, however, noticed that I'd also had floating adult-sim hair above the infant sim, so if you don't already have a broken piece of CC or a mod conflicting I'm not sure what your issue may have been.
If you look up "quianna curly babies" via google there should be a result for a blog that has some custom infant CC.
Pleasantsims also has a link in her blog to some infant hairs, I think.

You should probably remove the bad cc. Crincrit has great tutorials for removing bad cc here https://sims3.crinrict.com/en/custom-content-cc/bad-cc
the boots are probably the night time day time everyday boots, the first ones on this page https://sims3.crinrict.com/badcc/en/BadCC_Clothing.html.