Where are all the children spending Christmas Day? Ideally children in the same place at the same time need to be treated equally.
Had your DH put money aside for his children for Christmas? Or did he just plan to use his latest paycheque?
He could spend a day putting all the items for charity on fb market place, if they have loads it will soon add up.
Have you a slow cooker? He could set up an elaborate hot chocolate station pretty cheaply and make a sign for behind it so it's decorated really well.
He could also do a gourmet popcorn station, either in a wok or a very cheap machine with lots of toppings etc.
If you have a big cardboard box he can make it into a basket, wrapping in Christmas paper, as a movie night hamper, he could even do one for all three kids, it will look huge. Their favourite movies on dvd would be cheap from eBay or a charity shop.
He can make some tickets for a theme park for use in the summer. Them make sure he looks for offers to make it as cheap as possible.
There is lots he can do. There isn't a job he can get now which is going to pay him before Christmas, so he can use an hour a day researching and doing bits towards a more rustic Christmas this year. He also needs to sit down asap and explain it to them, they are old enough to understand money.
I would give your dd the laptop whenever they are getting their gifts at their mum, she doesn't need to wait until January.