With a little prep, it's the BEST option in my mind.
I have (2) kids, 4&2 yrs. repectively. We also own a Tahoe with all leather.
Now, I was way paranoid at first, but after numerous spills, puke sessions, etc, I am so glad I chose leather!!!
Here is why:
1. Leather is 'tanned' with H2O. Thus, wather actually cannot HURT it, if you don't allow it to 'soak' for long peroids of time. Also, there are some awesome products to help you take care of leather. (As a previous owner of a Audi S4, this was key!)
www.carcareonline.com is a awesome car care site, and they are EXTREMELY helpful on all aspects of car care, including leather maintainance.
2. I found a seat cover thingy at Target. It is bacially a felt lined cover, with a nylon insert to prevent seepage if you spill on it that sits on top of the bench seat, with some nice mesh pockets that hang over the front of the seat. I think it was about $10, and it big enough for the Tahoe, so would be perfect for the 6. This one has a edge with a sewed in raised insert that you slide into the slot created by the bottom and back of the rear set. I then have the car seats on top of this. WORKS AWESOME!!!!
3. Here is an idea if your REAL anal like I am. Child seats are quite 'straight' on the back support, where a car seat actually tapers inward away from the lower spine (if your sitting in the seat itself). To secure a seat you need to really puch the kids seat into the seat and tighten the belt, which can cause 'depressions' or 'wrinkles' in the leather. Here is what I did.
a. Bought (2) cheap black terry cloth towels.
b. Bought a strip of foam padding, about 1" thick from a local upolstery shop, I think I paid $3 for this.
c. Had the Mother In Law sew the towel like a pillow cushion, inserted the pad and presto... I have a pad that protects the seat leather! If they get dirty, pull out the pad and wash the towel!
Total cost, maybe $15.
Overall, witha little attention, leather is the way to go. Personally I love Pinnicle products (available at CConline... above); and Lexol is great as well and easily available at Target, KMart or ANY Kragen/Schuckers/AutoZone etc.
One final thing... if you do a little homework, you can actually increase the suppleness of your leather with proper washing and conditioning. It takes me an additional 20 minutes maybe once a month (In SoCal by the ocean, so I deal with heat and salty air); but my seats are like butter!!!!
and another... if your going with a new child seat, check out the one by Recaro.. it's is pricy but man is that thing built solid and easy to clean!