NC. I was the parent (mother!) who did this three years ago. DD was five. We had had an early Christmas Day with her older sister a couple of days before. Our work is usually very busy in November and December and I've never quite been motivated enough to start planning in October.
So - we had managed one mini-visit from Santa already, and delivered a sack of gifts to her cousins before making the five-hour journey to my in-laws.
I hadn't actually packed the little ones' presents yet - they were all in a black bag which I'd hidden in the junk room with all the other family gifts, already wrapped.
We got to my in-laws and I spent the afternoon icing a Christmas cake as part of my contribution. We put the family gifts under the tree.
At 9pm I looked in the car for the black bag to start wrapping. No bag. I checked and checked.
I started crying. So much so that I still had a headache in the morning. Nobody's fault but mine. I went through the same thought processes as OP. The drive there and back would be 10 hours through the night with a chance of not being back until 8am. DH had had some wine so couldn't drive. I was also still breastfeeding. My brother-in-law offered to meet us half-way but it was clearly ridiculous.
I remember my mother-in-law looking unconcerned and saying 'oh don't worry, she'll get heaps from us'. In their family, Father Christmas delivers presents rather than providing them - so there would still be scope for Santa to have 'been', just not the way I was used to.
There were some stocking fillers that I wrapped - which filled a very small stocking. My husband contributed the silver necklace he had bought for me. My MIL then suggested her spare mini-whiteboard, still in its plastic wrapping, with board marker pens. Not my finest moment: I said 'an office whiteboard?? Why not? Why not just wrap up some cutlery from the kitchen drawer as well'.
She said later that she had to leave the room to have a good laugh.
I carried on Googling desperately to see if I could get to Gatwick to buy emergency gifts. I can't remember why I didn't do this - I think I'd offered to drive to midnight mass and otherwise people couldn't have gone, and that mattered too.
The next day, there was my husband's family's traditional sedate unwrapping of gifts just before lunch and DD sat patiently on the children's stool until it was her turn. She loved her gifts. She had plenty. I asked what her favourite thing was - 'the whiteboard'.
When we got home, my family had found and wrapped the remaining gifts and they were there under the tree.
I still remember being really, really upset about this - but also that it turned out not to matter. The most important thing for her was that Santa had come, a sign she'd been good, and what the gifts actually were was not as important as I thought.
Like everyone above I can't quite understand the thought process of putting gifts under the tree at home (!!) but most of us have had a tough couple of years. When we're stressed and distracted we go onto autopilot and do the habitual thing just when you need to remember to do something out of the normal run of things - that's when we make mistakes.
I'm glad she's having a lovely day!