OP
There are a couple of other threads at the moment with similar things, but there is one about the best present ever received and lots of them are home made eg someone wanted a Wendy house, the parents couldn't afford it but her mum made a cover for the table that turned it into a Wendy house.
One I saw from MME and has been repeated for your 2 year old, get a box, get pack of balloons, blow up the balloons and put them in the box, it's something really exciting when you are 2.
You can get odd half rolls of wall paper, you can pin / staple / blue tack it to your wall so you have one wall that is blank, then let the kids draw on it, imagine having a whole wall to draw paint on?
Do they have any jobs (obviously not the 2 year old) a voucher to be let off doing the washing up or tidying a room that can be used later in the year.
A voucher for an afternoon / evening with just a parent to do an activity as a voucher, with three it can be difficult to get time one on one.
Have a look in the discounted aisle of shops, and go into places you would not normally go, I got a summer tent for a teenager for £2 a couple of years ago.
Clothes from charity shops or jumble sale (do they still exist?) in a big box (you can use some of that left over wallpaper to decorate) labeled 'Dressing up', another one with craft / art supplies - smaller box or a tool box.
Actually boxes can become boats, TV, theatre, evena drive through.
Does your budget include Xmas food? If it does get a big box to make as a counter or drive through and let the kids order off the menu of burgers and fish fingers you have put up, you can then serve burgers and fishfingers and it be the best Xmas meal ever, obviously tailor to your children's taste. Oh and wrap the burgers in Xmas paper if you have any left.
If you order from Amazon and ask for gift wrapping you get a bag with sparkles on it that can be filled with other things.
Wooden spoons are cheap and can be part of a home made baking kit or used with a theatre made out of a box and clothes made from the craft box.
Actually I had a childcare class make puppets and then make a film showing things like going into hospital, or going to school.
I'm not suggesting anything educational but if they make a puppet show it can be filmed and put on YouTube.
I think the key is to think like a child. Don't think about anything being second hand, not in a box, or cheap.
Think of the excitement.
Have you heard of Tió de Nadal? Basically it is a log with a face, it is covered with a blanket to keep warm and fed for several days (you could start Dec 1st).
On Xmas day, or Xmas eve the children have to leave the room to get or warm sticks in the kitchen.
They come back and beat Tio with sticks, sing to him and tell him to poo.
You then remove the blanket and the 'poo' is sweets.
Now to an adult that's just a log, but the combination of telling a log to poo and then finding it has pooed sweets or biscuits is funny.