When I was doing my PhD, I would leave wrapped gifts at the door of every child on Christmas eve as many student parents couldn't afford much during the holidays. My husband inexplicably found this hilarious and always wanted to know what went where so he could 'track results.'
One child in an upstairs apartment got given a dance mat.
I gifted one family with five children a pottery wheel with a selection of clay options and a book where you check off every creation you make (totalling about 150).
I got one energetic young boy a baseball bat, a ball and a thing to hit if off so he could practice in the car park.
A remote control furry hamster that sung in a high pitched voice as it drove around, provided with a big pack of batteries (nothing worse than having no batteries when you get a brand new toy)
A bezazzling kit with lots of extra glue so they could make everything sparkly.
A prank kit that I didn't check the contents properly of and it included 'buck urine' which stinks. You could DIY this if not available in your area.
Toy chainsaw for a child whose dad was doing a PhD in something to do with firebreaks/forest management. It was louder than I anticipated.
Tamagotchis the first year they came 'back'
I wish he'd told me I was creating enormous upset, but I did enjoy being the mystery Father Christmas for four years.