We are all big readers in this house and so the Little Library sets that you can buy in John Lewis and Tesco and Asda (and other stores!) are great buys. As the Little Library sets are normally featuring children's favourite characters from favourite TV shows I know that they will go down well with Baby Boy.
Top Ender is really into the Rainbow Fairy series, as mentioned in my blog post about Helping Children Learn to read and a couple of the series will no doubt find their way into her stocking.
Granny likes the books by Torey L Hayden (and others in the same genre) and so there will be a book or two for her from Santa.
What kind of books will you have in your stocking or do they go under the tree instead?