Do you mean you want to download old books HERE, from the SCM site? This site is largely not for that sort of thing, though there are some free PDF and ebook resources available here, as well as previews of materials for sale.
I have had lots of luck finding great old books at Project Gutenberg, OpenLibrary as well as a site that lets me download books directly for my ereader called Feedbooks. Google any of these and you’ll find thousands of classic books to share with your kids.
Hope this helps!