To Rebecca McNally at Macmillan Children's Books, three authorised adventures by Andrew Lane about the young Sherlock Holmes. Book one, THE COLOSSAL SCHEMES OF BARON MAUPERTIUS, is set in the 1860s, when the 14-year-old Sherlock is sent to spend the summer with eccentric relatives as his soldier father heads for India; the boy genius "is drawn into a sinister international plot with a brilliantly imagined villain at its heart". Lane, a lifelong Holmes fan, has written tie-ins to Torchwood and Doctor Who, as well as ghostwritten books. McNally says: "Andy's written a completely gripping thriller which takes the world's most famous detective and turns him into an utterly convincing, psychologically complex, flawed, clever 14-year-old boy."Read more about the plot(s) in The Guardian.
Last year Hodder Children's Books published Tim Pigot-Smith's The Dragon Tattoo, the first of the Baker Street Mysteries in which Holmes has disappeared. The follow-up, The Shape of Evil, is due out in October.
There is also a children's series by Tracy Mack and Michael Citrin about Sherlock Holmes & the Baker Street Irregulars which currently has 3 titles (US publisher, but available here through amazon.co.uk etc).