Like the countless MLM business out there, you have chance of ending up with unsold stock, I wold worry about too few sales opportunities, you may have to offer aq wider ariety of products to make a spot in a more general show pay off. Though books stores have been going out of business I suppose kid books will never be completely replaced by electronic readers.
Do consider if you just bought and sold books as a completely independent business is it possible to be more profitable, while not being tied to a single supplier.
A couple of kid book wholesalers
http://www.dollardays.com/wholesale-childrens-books.html
Direct from China, for high volume sellers
http://www.alibaba.com/showroom/wholesale-children-books.html
Their retail outlet
http://www.aliexpress.com/w/wholesale-kids-book.html
I found few negative opinions about usbourne on the internet, but do bear in mind recruitment is a top priority with these MLM businesses, so a lot of endorsements are by those looking to share your revenue.
There are almost universal recommendations in this forum thread:
http://www.netmums.com/coffeehouse/working-childcare-692/working-689/928223-usborne-books-worth-all.html
A teaser review that seems like it may be reprinting the company literature
http://www.businessopportunitywatch.com/review-usborne-books-at-home.htm
An early mention of the 15 year old business.
http://www.theguardian.com/money/2002/mar/17/workandcareers.observercashsection