Next year buy a lovely calendar without candy, just with pictures. This is what I do, because usually the candy is very low quality anyway.

OP I read your followups. Just ignore the tantrums. Tantrums are actually okay. It's okay for them to feel overwhelmed. Hug them and acknowledge how they feel. They also don't like to feel out of control, so talk about what they could do differently next time (kindly). Just keep working through the tantrums and not giving into them. DH and I just repeat to each other that we don't negotiate with terrorists.

Some kids do need more encouragement and are harder. My DH has ADHD, but he's channeled it and is very successful. ADHD people actually have incredible focus. My youngest is giving us a run for our money and I can already see he has more of DH's traits, but that just means we'll double down.

Buy this book, OP.
https://www.amazon.com/Your-Four-Year-Old-Louise-Bates-Ames/dp/0440506751/ref=sr_1_1?keywords=your+four+year+old&qid=1575575071&sr=8-1

I literally cannot imagine thinking this was an actual issue and ruminating on it this much. You need to start a gratitude journal and I really, truly hope you do not encounter any actual hardships or illnesses or disabilities with your kids - but you are going to, so I suggest you think about some resilience building. She is a preschool aged child. She did not spring forth fully formed from your head. Put some work in. FFS. If I knew you in real life I would have been rolling my eyes so hard at your advent calendar whining.