Madcap rhyming seems to be the order of the day for early readers this season.

It is only now that one of my sons has reached the right reading stage that I realise the sheer genius of Tim Healy and Chris Mould's Mortimer Keene series. I have never seen him devour a book with so many tricky words so fast as he did Mortimer Keene: Ghosts On The Loose (Hodder Children's, £4.99). Mortimer Keene, we are told, is a small kid with big ideas, and his stories seem to be designed for small children with an appetite for big words. But it is the zany comic writing and elegantly ghastly pictures that are the joy. In this story Mortimer creates a phantom machine, which churns out ghosts.

Squishy McFluff: The Invisible Cat by Pip Jones (Faber & Faber, £5.99) is also in the tradition of rhyming fun for the young. The title might make it sound too much like it is a Lynley Dodd wannabe in which Slinky Malinky squishes into Hairy McLairy. But actually, the name is just right for a story following a character who is really a little girl's imaginary friend - "a fabulous, friendly invisible cat". Naturally, as with all imaginary friends, Squishy tends to get blamed for "all manner of mischief": when the table gets covered with pepper and salt, Ava says, sweetly, "It's all Squishy's fault". Delightful illustrations are by Ella Okstad, with Squishy portrayed as a big-eyed bundle of cuddly lines, barely there, a visible invisible swirl.

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The Pointless Leopard: What Good Are Kids Anyway? by Colas Gutman (Pushkin Children's Books, £7.99) was a hit in France where it was made recommended reading for 6-7-year-olds. Of course, being French, and with a title like that it is poetic and a little philosophical. Leonard does not like the countryside: "It's ugly, it's green and it's boring". All there is to do is admire, which is "the same as being bored, but with your eyes open". Things, however, get a bit more entertaining when he comes across a talking sheep who wants to know a little more about exactly what kind of creature he is. Bottle opener, sewing machine, blender? As much for the adults, I think, as the kids - but charming, nevertheless.

One welcome diversion from the relentless diet of the fantastic and imaginary that often seems to dominate the children's market is Michael Foreman's The Amazing Tale Of Ali Pasha (Templar, £12.99), a book that is a simple, almost journalistic, telling of a real life tale - that of a tortoise found by a naval sailor while fighting in Gallipoli. There will, no doubt, be other books about the Great War, but this is Foreman, author of War Game and War Boy, the master at striking the right tone. Here, he tells the tale of Henry Friston, who when lying in a crater following a shell blast found himself knocked on the head by something that "was not a shell, but a tortoise shell". It's a wonderfully layered piece of storytelling, using diary, photographs, delicate watercolour illustrations, plus an invented journalist, to tell the tale - but what is important is that he gives a sense of connection, an awareness that there are people alive today who met and were inspired by those who fought in that war.

For 8 to 12s, A Pig Called Heather by Harry Oulton (Picadilly, £5.99), set somewhere in Scotland, is a story about a rather clever pig called Heather in the grand tradition of stories about clever pigs. Heather does not talk to humans - as she does to other animals - although she does squish up her nose, fetch things and generally behave as a loving companion to Isla her small human friend. Written in a matter-of-fact third person, it ambles along inside the homely head of the pig, who works at a rather relaxed place and considers that "doing nothing might be even nicer if you could think about nothing while you were doing it". Although Heather's mind may dawdle the story rollicks along, a moving tale of friends parted.

The Islands Of Chaldea, HarperCollins, £12.99 may not be Diana Wynne Jones's absolute greatest novel, but the fact we have now, after her death, one more of her magical books is a treat. Wynne Jones died midway through writing this, and though it is not all her own work, it is hard to tell which part was written by her sister Ursula Jones. Like many of Wynne Jones's stories, this is a quest tale, one set in a magical and alternative British Isles, with Skarr (Scotland), Berenica (Ireland), Gallis (Wales) and Logra (England) all islands cut off from each other by sea. It begins with the comforts of porridge, which is wise woman Aunt Beck's "answer to everything". But the book's real pleasures, as always with Wynne Jones, are its beautifully wrought, iconic characters: short, clumsy Aileen, who is always frustrated with her own ineptness and inability to become the wise woman she is destined to be; immaculate Aunt Beck, with her red boots with cork heels that never seem to get a splash of mud.

Debut novel Who Framed Klaris Cliff? by Nikki Sheehan (Oxford University Press, £6.99) is a rather clever idea, deftly executed, and set in a world where, following a mass killing in a school, in which imaginary friends have been blamed, such companions are banned. When discovered they are removed by a procedure known as the Cosh, in which lasers are used to shrivel parts of the brain. Actually this is also a domestic whodunnit, examining who is responsible for various household crimes, from plying the dogs with alcohol to shortening a stethoscope chord. Particularly charming is that Klaris Cliff is about the least fantastic imaginary friend one could develop - annoying, practical, a little bit boring and almost entirely sensible.

The market for fantasy thrillers featuring 13-year-old boys seems to have gone into overdrive this month, with a slew of novels that declare they are for fans of Michael Grant's Gone series. Two of them, The Blood Guard by Carter Roy (Scholastic, £6.99) and Thirteen by Tom Hoyle (Macmillan, £6.99), are written by authors who have taken pseudonyms and chosen to hide their real identity: Hoyle, the headmaster of a London boy's school; C Roy, a "memoirist and award-winning short story writer".

It is Roy, however, who seems to have revealed himself a virtuoso in the form. In The Blood Guard, Evelyn Truelove has been living a relatively normal life - apart from the fact his mum schedules all his hours with extra-curricular training in "everything from judo to aikido, Krav Mags to kendo". What was all this about? Preparing him for his future, as he finds out after his mum picks him up from school and tells him, mid crazed car-chase. Mum it turns out is a dab hand with a sword and a member of the Blood Guard, a special organisation of warriors set up to protect the pure souls that keep the world in balance. The book has movie written all over it, right from the pre-credits with a house going up in flames. But it is more than that - it is slick and witty with a touch of literary flair.

In the young adult market, the two stand-out novels are those dealing with real and darker, more difficult areas of youth existence: teen pregnancy, in Trouble by Non Pratt (Walker, £6.99); and having a difficult brain condition, in When Mr Dog Bites (Bloomsbury, £12.99), by Coatbridge author Brian Conaghan. "A boy, a girl, a bump," is the tag line for Trouble, and Pratt's prose is casual, effortless, not too flashy, as she tackles her subject in a funny and non-judgemental way. It is partly a tale of friendship - but also a portrait of being teenage and pregnant, or having any kind of sex life, in the age of savage social media.

When Mr Dog Bites, meanwhile, is part of a recent trend, started with Mark Haddon's The Curious Incident Of The Dog In The Night Time, featuring young protagonists who have some kind of mental condition. Dylan Mint's "Mr Dog" is Tourettes, and it erupts like a volcano of profanity from time to time. Conaghan, it turns out, has this condition himself, and there is a sense of exhilarating authenticity in the wordplay of this his second novel. But I am not sure how convincing it is as a portrait of a young man who genuinely thinks he is going to "cack it". Some of the dark places of this territory seem to be absent - as they are with Trouble. Does that matter? After all When The Dog Bite's breath-taking pleasure partly is that it manages to make a difficult subject charmingly feelgood. "Heart: swollen," writes Mint at one point - and I felt that too.