2. Fantasy fiction, carefully chosen, may be a good option. Eva Ibbotson's fantasy fiction for younger children and Diana Wynne Jones' Chrestomanci series are good options, as well as the first three Harry Potter novels. (Some parents may consider that the later ones are not appropriate for their children; some will not be unduly upset, but others may find them frightening, as well as very long!) I particularly enjoyed Lucinda Hare's Dragonsdome Chronicles novels last year, which combine the close relationship between children and animals that I enjoyed in pony books as a child.
3 Animal stories, such as those by Michael Morpurgo, Dick King-Smith and Lauren St John are very enjoyable. Some parents may consider some of Michael Morpurgo's books too challenging for younger readers, but the synopses on the website should give a good indication for your children.
4. Classic children's books. The Narnia books by C.S. Lewis, Noel Streatfeild's novels (and children who enjoy them may like Lyn Gardner's Olivia books) and Arthur Ransome's Swallows and Amazons may be enjoyed by younger readers. The narrative drive of the stories may over-ride the historical setting and unfamiliar language.
I hope that these suggestions are helpful; thank you to the tweeters named above for their suggestions which inspired this post!