I visited your website and thought I would share my feedback. It is a smart idea that I know many families would like to take advantage of.
We are a family of readers. Books are practicaly a food group around here. We devour them, inhale them and therapeutically read our favorites over and over.  Here are the reasons I don't see this program as a good fit for my family-
1.) $25/ mo is way more than I am willing to spend on books I'm not planning to keep. I simply can't justify renting a book for $2.50 when I won't spend more than $1.39 on a movie. And while I think it's nice that families can keep them for several months, the subscription no doubt continues to charge the $25/mo fee regardless of how long you keep the books. Assuming it takes 5 days to process and ship and order, and a family has the books for two weeks, then another 3-4 days to return ship, then five more days to receive the next shipment. I don't see how many families could get, read over and over like children like to do, return and receive again any more than one shipment a month. It's quite expensive. I have subscribed to book clubs where I received at least that many books per month for less money, and we got to keep those for good!

2.) In my experience children often enjoy most that which they select them selves. This is part of growing good readers. Each of my children received their own library card when they turned five. They love the library, and they often pick out things I never would have found. As they grow this is priceless in helping them to enjoy reading. The library is a treasure chest of ideas, adventure, and challenges. Rarely have I ever brought home a book from the library and thought 'man, what a disappointment.' To expedite one's visit, parents can look for recommended books online prior to their visit and some libraries even accept requests over the phone or online so you can have specific books waiting for you to pick up. Children's librarians can be a wonderful resource for recommendations as well.  I am sad for all the kids I know who have rarely been to a library, it is a sad reflection of the dominance of technology in our day. If you can take your kids to see a movie or out to eat, surely you can maneuver them into the library at least once a month. ( don't forget that libraries have after hour drop boxes so items can be returned anytime, no packaging or shipping involved)

3.) I didn't see any guidelines for when a book gets damaged while in one's care. Children are often unintentionally rough on books. Accidents happen.

I think this program has potential. But if you want my family's participation I would have to see more from the program. For example, I think that a more reasonable monthly price would be more appealing and affordable, say $14.99-17.99 range.

Or perhaps a family only pays per package instead of monthly, then the price seems more reasonable, especially if the books are kept longer than just a week or two as I image most are. 

If you truly wanted to be the Netflix of books your price could include a limited number of digital downloads.

Also your age range is very strict, expansion of this could allow you to offer more than one package or even multi-packs at a best deal price.

All in all I think it's a cool idea and you will no doubt have plenty of success in your venture, but I think my family will continue enriching our reading for free at our local library.