I'd go with CWU. It's modular, so any damaged sections can be easily replaced.

As for the baby, I'd mostly be worried about them putting parts of the castle in their mouth. Besides the obvious choking hazard, the printer ink and/or glue may be toxic.

I'd second CWU. Its more impressive, and you can do more things, such as the curved walls, archways, building interiors, moats, etc.

How does the build time compare between CW and CWU?

I've looked at the non-paper castles, but the wooden ones are prohibitively expensive ($30+ for small block sets, $100-$150+ for quality sets) and the plastic ones like Legos are still expensive (the viking fort is $70) and have a lot of small pieces that would be choking hazards for the new little one. I'm kinda thinking of this as a supplement to their main birthday gifts, something that I can do relatively inexpensively ($15-$25). If I had a suitable wood shop set up at the house, I might have tried building one out of wood, but I don't have the space or money to set up a shop at the moment.

Whenever I leave my WWG stuff out on our big gaming table, the girls have a blast playing with it and are fairly gentle (I put more wear and tear on the pieces than they do). My soon-to-be 7 year old is also interested in starting to play RPGs, she is in first grade but does math on a 4th grade level and reads on a 5th grade level. I can see giving them a pre-built castle set as a good introduction to the cardstock modelling; knowing them they will soon want more pieces or will want some fixed/replaced, I can use that to teach them how to build it themselves (I'd probably still do the cutting and scoring, I don't think Xactos would be safe for them yet).

I think making it will have much more sentimental value for them, and for you.

My 6 year old likes my cardstock stuff, too, and she is pretty gentle with it. Of course, she's munged a piece before, so she now knows how much pressure she can actually apply to a piece. I've even made her an Ebbles floater or two for her D&D minis, and she's asked for more - she even wants a full FirstLight like mine!

Hmmm.... that isn't a bad idea for your kids, actually - make a piece specifically for them to mash up, so they can get a feel for how fragile their new castle is.

Ah, I forgot the choking hazard and expense problem.

I think a good solution would be a paper theatre. There's a nice one here for a nickel less than $20:

http://www.scienceartandmore.com/index. ... rodID=2425

http://www.scienceartandmore.com/browse ... eatre.HTML

If you want to print it yourself and constuct it directly for the girls, there are a bunch of ones at the Fishmarket theater site in the Netherlands. The latest is an Alice-in-Wonderland one:

http://www.vischmarktpapierentheater.nl/Downloads.html

There are spotty archives of older issues of the website/online magazine:

http://toytheatre.info/Archives/VoorGigi/Index.html

At very least, the page with the cutouts of the Alice characters is cute and something the girls can play with without any trouble if the little one eats things, or at least no worse than any piece of paper.