You're right - little kids do not properly appreciate contributions to their college funds. :^)
Here are my standard gift ideas: Books can be great. Supplies for drawing, painting, work with clay can be great. Crafts can be great. Do your older children have a particular interest? That's a good lead.
With my children, and now with my grandchildren, I realized that they didn't mind not having the fancy, big-ticket things (not being promised those things!), but they did like having presents to open. An outfit for a favorite doll makes a nice little package. So does a box of Legos, or a set of drawing pencils along with a tablet of paper.
Another idea for grandparents, aunts, and uncles, if they live nearby, would be a trip with them to a museum or a show after Christmas. If they don't live nearby, they can send the parents as well as the kids.
You might talk to your children and ask if there are toys (in good condition) in their rooms that they think it would be good to pass along to other children whose parents are out of work and won't be able to buy them toys. Children can be incredibly generous when they are given the chance.