I hadn’t heard of them at all until a few years ago, but will confess to buying them for little Gdcs when they were coming here for Christmas a couple of years ago - very cheap flat pack cardboard jobs from The Works, and I just put in them some Christmas plates and mugs (to come out again every year) and a couple of books to read on Christmas Eve - The Night Before Christmas, and a simple Nativity one, again to come out again every year.
There were a few other (non plastic) bits, IIRC some new pyjamas I knew they could do with, but not particularly Christmassy ones.
I’ve recently bought them a really lovely Christmas book - The Empty Stocking* - is anyone else familiar? but it’s too good to save until Christmas Eve - they’ll have it as soon after 1st Dec (or Advent Sunday) as I can get it to them.
*perfect for their ages IMO - 4 and 5.
No. 3 is still too young for such things, but I’m sure she’ll enjoy it later.