[2020] Low residential - unhappy households made of children

Hmm, that does sound strange. :S Can you share your output log (player.log on Mac and Linux)? That would be the easiest way for us to have a look through your mods and see if any combination might play a role here. This guide explains where to find it and recommends some sites you can upload it to, as we can't attach files here on Steam.

https://steamcommunity.com/sharedfiles/filedetails/?id=463645931&searchtext=log

Sharing your save to the workshop would be another way we could help investigate what's going on here. You can do that through the Content Manager in game, by finding it under Savegames and pressing the Upload button. Then share the link to the save here.

I just had a look through your mods and I suggest removing these two and testing how the city works without. It might mess up some things depending on how much your city uses those two mods, but the interesting part is if it fixes the households that seem to be stuck.

Customize It Extended
Ultimate Mod 2.8

Ultimate Mod is pretty new and so might have some undiscovered incompatibilities with other mods, as it does a bunch of things at once.

I'll load up your save once I get a chance. It should be fine with the mods and assets you have. I play the game heavily modded myself, so my system should be able to handle it. :)

Hmm, that could very well be related. Could you try and trigger the error and then upload the output log from that attempt? With a bit of luck that error will give some idea of what's going wrong.

Ah that's good to know! Could be it's needing an update.

There's always the option of Force Level Up. It takes a bit longer, but it'll get you there too. And afaik it works like it should without any weird things happening.

https://steamcommunity.com/sharedfiles/filedetails/?id=523818382&searchtext=+Building+Level+Up