This probably has happened to others or has been brought up before, I just couldn't find anything.
At 1:00 when my 2 teens come home from school, the first one starts getting off the bus and the game freezes for a few seconds, then all of a sudden the schoolbus vanishes as if it's been deleted and all 3 kids (the child that's supposed to come home at 3pm) are standing in front of the house, homework-less. I've moved the whole family to 2 different houses, and even deleted the kids, saved the game, and came back into the house - no change.
I realize it's probably some CC installed in my game that's not playing nice with other CC but does anyone have any suggestions? Thanks!!

Are the parents alive and living on the lot? If not, you probably ran into the 'get parents' bug - the kid tries to cheer and show their parents the report card, but there isn't any parent so they just get reset instead (which also poofs the bus and homework ). Here's the fix.

Yep, the parents are alive but not home at the time the teens get back from school. And yes, as a matter of fact, the teen is cheering and runs towards the garage (not sure why though) then stops short, the bus and homework disappears and the child Sim suddenly appears. I'll try that fix, thanks!

I've only seen the error when the parents were absent/dead (e.g. the Newson family), but it might happen in other circumstances. You can check this by turning on testingcheats before they return home - you'll get the error rather than an auto-reset then.

Your fix worked! Thanks alot!