I'd go for a Rail Fence as well.

I would have them start looking at ideas and then run them by you to see if they are "beginner " patterns or not , a lot may depend on the fabrics they may choose as well . I love to plan so I had to chip in again lol
Be sure and let us know how it goes and of course take lots of pics for us !

I like all the BQ patterns. They look complicated but are easy to do. The blocks are good sized, they'd get practice in sashing and matching corners. Because of the big blocks, it goes together quickly.

A simple, small sampler using Rail Fence, Log Cabin, and a Nine Patch--making 3 of each and putting them together their own way would be fun.

Yellow Brick Road is a great beginning pattern.

Double Irish Chain is easy and makes a beautiful quilt, or a Churn Dash block, each one in a different colorway, but with same back ground fabric.

If they aren't real confident sewers... just buy some charm packs and sew scrappy style, or no particular order. That way they can get the feel of the process and go through all the steps. If you have a stash of some yardages that look nice... they can cut their own. Bigger pieces are more forgiving than small. If they are up to it Yellow Brick Road is a great beginner quilt.

http://www.incolororder.com/2011/08/...-tutorial.html

I'm in the middle of this one, I am adding boarders to it in order to make it a queen size, but the basic star goes together in no time and is easy to cut and sew for beginners.

Daughter did a Quilt-in-a-Day quilt from a book the same title when she was eleven (she preceded me quilting by twenty years!). I do not remember if "in a day" including the cutting of the pieces. It was beautiful. And very adult.

How old are your daughters? Age will make a big difference in your choices. If they're young then precut and simple is the way to go, if older then ask them what they would like. Maybe talk to them in advance to make sure you have fabric in the colors they like available (more time sewing and less time shopping) and maybe pick a few beginner patterns to have ready for them to choose from.
Rodney