I know this is late but I can't resist cheering you on with a few more ideas to consider. ;)
In Utah, there is always Christmas Box House, which provides shelter for children before they are matched with a foster family. They always need birthday party items, since many kids are stuck there when it's their birthday, and many have never had a real birthday party. If your family celebrates the religious aspects of Christmas, you may enjoy talking about the Savior's birthday and combining that with choosing birthday party items for kids at the Christmas Box House.
There are also numerous women's shelters which serve children, too. The one I am most familiar with is Safe Harbor in Davis County. They always need items to keep moms and children comfortable while they figure out where to go next.
The Human Society of Utah graciously accepts donations to help homeless pets there. If your kids like animals they may really enjoy helping out there, and many of the siuggested donation items are cheap and easy to get (cat litter, newspaper, etc.). Could be an opportunity to talk about helping places that provide shelter to people and pets who do not yet have permanent homes, and how Mary and Joseph were a little bit displaced in crowded Bethlehem and could have used some help, too.
Finally, have you looked into Heifer International? It may not meet your criteria of being able to see firsthand the difference you make, but it is pretty amazing. Their on-line catalog explains in detail how your donation is used, and you can choose what sort of animal (bees, sheep, goat, cow, chicks) to gift to a family in need who can use it to sustain themselves and help their community's economy. www.heifer.org, I think, is their Web site.
Best wishes!