This is what I told someone from several weeks ago.
You have several options. A good many collectors use eBay to find books, so if you are willing to use eBay, that is the easiest and fastest option. You would list the books in an auction, and if your starting bid is reasonable, the books will sell and will go to a good home.I could tell by the response I received that she did not like my answer. She did not want the library to sell them for $0.25 each as she thought that the books are worth more than that. Why would the library's selling price matter? The fact that she was concerned about the price tells me that she was not going to want to sell the books cheap. I do not need the books for my collection, so I am the last person to approach if someone wants good money for their books.
If you do not want to use eBay, then you could sell your books to a local book store. They might pay less than eBay, and it also depends upon how desirable your books are to them.
Another option is to donate them to your local library. In this case, the library would probably not shelve them but would instead sell them at their library book sale. In that case, the books would eventually find a good home.
She also made the comment that she did not want to risk the books ending up in a six-year-old's hands. Why worry about that? We cannot control who buys our books or what they do with them. In fact, if you sell me books, they may very well end up in a six-year-old's hands. I do not worry about what people do with the books I sell or how old the recipient is. I know that I have sold vintage Nancy Drew picture cover editions to people who have bought them for their grandchildren. I doubt that those grandchildren are adults. The children might abuse the books, but that is not my problem. I cannot police the world.
I also do not think she was very enthused about eBay. Well? It is the best option. If the books do have value, then I did her a favor. She will get more for the books than from selling them to me.
Since that exchange, I have decided that I could simply ask for a photograph while advising that a high chance exists that I would not want the books. If I do that, then I will not miss out on any good books but will not have to spend time seeking information about books I do not want.