'The Year That It Rained Cows': The silly, strange and fascinating world of books for the under-12s

This being the silly season, we should perhaps begin with a very silly book. Philip Ardagh writes funny like he can't help it, and in his new Grubtown Tales series for younger readers (Stinking Rich and Just Plain Stinky and The Year That It Rained Cows, both Faber, ?4.99) we meet ludicrous characters with preposterous names (our young hero is a boy called Mango Claptrap) to whom outrageous things happen. Silly, silly, silly. Young readers will love them. (Old readers, too...)

The Raven Mysteries is another new series, this one from the pen of Marcus Sedgwick, already known as one of our best writers for teenagers. It begins with Flood and Fang (Orion, ?7.99; also reviewed as an audiobook on page 25). Edgar, our raven narrator (below right), lives in Otherhand Castle with a hopeless family who keep needing Edgar to come to their rescue. In this first book, the peril comes from a flooded castle and a prowling scaly monster. Edgar is grumpy, self-important and extremely good company, and the family is as mad a bunch as you could hope to meet in a fantastical castle (including the delightful Solstice who says "Gasp!" a lot, and her brother Cudweed's disagreeable monkey). The series continues this autumn with Ghosts and Gadgets.

Tanya Landman, another acclaimed teen author, has launched a series of brief, brisk, exciting murder mysteries for younger readers, which begins with Mondays Are Murder and Dead Funny (both Walker, ?4.99) They feature the resourceful Poppy Fields, who is surrounded by multiple murders wherever she goes and must work out what on earth is going on, assisted only by her friend, nerdy Graham. They are short, quick, easy reads, action-packed and dosed with a pleasing amount of gruesomeness.

Among the many follow-ups to recent successes, two – very different from one another – stand out this season. Toby and the Secrets of the Tree (Walker, ?9.99) picks up where Toby Alone left off last year. In this second volume – the inspiring story of tiny hero Toby Lolness and his family, who face a crisis in the tree where they live – Timothée de Fombelle brings his lovely, original tale to a satisfying and heartening conclusion (with an important, but not over-weighted, eco-message), all impeccably translated by Sarah Ardizzone. From Anne Fine, whose The More the Merrier did Christmas misanthropy with such hilarious relish, we have Eating Things on Sticks (Doubleday, ?10.99). Harry's irresponsible uncle Tristram takes him on holiday to a middle-of-nowhere island. Can it possibly be as grim as Harry expects? A lively, witty, rain-drenched tale full of big beards, from one of our best children's writers.

Of several fine debuts this year, one of the outstanding new voices for readers in this age group is Michelle Lovric, whose The Undrowned Child (Orion, ?9.99) appears this month. A mysterious tale set in an alternative historical fantasy Venice – with mermaids – it is gripping, elegant and original. Michelle Harrison's debut, The Thirteen Treasures (Simon & Schuster, ?6.99), an engaging fantasy adventure with some rather startling fairies, won the Waterstone's Children's Book Prize. There's promise of a sequel on the way.

To conclude, a pair of significant conclusions. Caroline Lawrence's Roman Mysteries come to an end this summer with the 17th title, The Man from Pomegranate Street (Orion, ?9.99). Our old friends Flavia Gemina and co investigate again; this time it all starts with the suspicious death of the Emperor. Lawrence steers this story – and the series – to a romantic and irresistibly weepy conclusion, and, like so many good endings, it involves breathless reunions, a journey and a wedding. (I mustn't reveal any more...) It's happy, but it's bittersweet, too, as loyal readers have to say goodbye to Flavia and their friends for what may be the last time.

Meanwhile, Paul Stewart and Chris Riddell pull out all the stops for The Immortals (Doubleday, ?12.99), the 11th and final volume in their massively popular Edge Chronicles. It's a huge adventure-packed novel, filled with delights for the series' many, many fans, not least that extraordinary world and its creatures captured in Chris Riddell's endlessly beautiful, bizarre and marvellously detailed line illustrations. A real summer treat.