Hi Jennifer,
Port Orleans French Quarter is my favorite Moderate Resort for the reasons that you mentioned, especially the fact that it is the smallest.
That being said, if I were bringing two 6 year-old little girls, I would book a Royal Guest Room at Port Orleans Riverside in a heartbeat. Those rooms are absolutely exquisite. "The story behind these lush rooms is that Princess Tiana (“The Princess and The Frog”) invited some of her royal pals – Belle (“Beauty and the Beast”), Jasmine (“Aladdin”) and more – for a vacation getaway. Princes and princesses of all ages can enjoy their luxurious lodging quarters, which will include ornate beds that feature headboards with fiber-optic special effects, and gold and crystal accents. Guests also can enjoy artwork and special mementos left by Tiana’s royal friends." To see a picture of how these rooms will look, you can see
THIS POST on the Disney Parks Blog. I have heard so many wonderful things about these rooms and I just know that your little girls will absolutely love them. While the Riverside is a bit bigger, it was actually rated the favorite Moderate Resort in a poll of the entire Moms Panel. You'll enjoy the ferry boat ride to Downtown Disney and the property itself is beautiful.
You can't go wrong with either of these, but since you have two little Princesses to please, I vote for the Royal Room!
Have a wonderful vacation,
Kaylene