I have this bug myself playing Dowon. It happened all of a sudden, I think, after the newest update. First time I played InZoi after it updated, my zoi drove to the resale venue and this NPC is also a toddler.
I have already created my own support ticket and submitted my save files, mod saves, and other relevant information, so I hope they address it soon. For now, I don’t know what to do for my zois that want to sell their materials or resale things. 
If your save file is big like mine was @Sadgirl, create a support ticket here. Go to Submit Request and then follow the instructions here on how to compile the right information to send to support. 
I really hope we both get this bug resolved with time!