I am so glad to see all of these resources. I have been looking for things as well. I will be looking into the above suggestions. It is hard to find things on your own!
Recently I ordered Magnifikid from the people that put out Magnificat. I think 5 years old may be a little young for it, I will be using it with our 6 year old (starting tomorrow actually!), and I think that is the youngest I would start with it.
Magnifikid is a little booklet for each week that has the Sunday Mass readings and order of the Mass for the children to read along, a misselette in each issue. Also in each weekly booklet are a few activities and explanations of things in the Mass, readings, and prayers, also explains some vocabulary in the readings and prayers. I have been looking at our one we start tomorrow, and I can tell I will be learning things in it too.
I am really happy with it, hope our daughter is too!
Here is a link if you are interested:
magnificat.net/magnifikid/index.asp
A great online source for activities, we have used a few times and have liked all the ones we tried, is Catholic Icing, written by a Mom:
catholicicing.com/
We did some Thanksgiving, Advent, and Lent activities from there and enjoyed them.