How old are they? Would you want to give them books? clothes? toys? music? art supplies? trips to a special place like museum, zoo, science center? Does the rest of your family know your situation (assuming you have family)? If you are religious and have a worship community, will they know of your need? Have you attempted to register for Toys for Tots, the Salvation Army Christmas store, or any local group that helps with Christmas celebrations?
Do you have sufficient food to make a special meal for the day? One thing our family does is to make a gigantic yeast cake whose recipe comes through my husband's grandparents. Very special and saved only for December, yet inexpensive as long as we are not too indulgent with the poppyseed or walnut filling. Oh, it can become more expensive if we fill it really full, but that is not the way Bubba made it.
One batch makes enough to share with all his huge family, too. Start a tradition like that (if you have not already) and then there is something wonderful and memorable for every Christmas whether you are religious or not and whether you have money to buy gifts or not.
Definitely there are a zillion inexpensive holiday traditions you could take up for your own; my yeast cake is just an example. Making paper ornaments, stringing popcorn, decorating pinecones, going to a free holiday concert, learning to play and sing carols, going out carolling door to door...
Maybe if you could explain what it is you are hoping for, someone will have some ideas for you.