What was this book (time-travelling kids, an old house, a wizard, turning into animals...)

Sounds (very) vaguely like The Box Of Delights. Also a classic BBC kids Christmas serialization.

A magical old man has asked Kay to protect the Box of Delights, a Box with which he can travel through time. But Kay is in danger: Abner Brown will stop at nothing to get his hands on it. The police don't believe Kay, so when his family and the Bishop are scrobbled up just before Christmas, he knows he must act alone . . .

John Masefield’s classic children’s book is considered to be one of the great works of modern children’s fiction. Magical, fantastical and filled with vivid, rich characters – brought to life in this edition by Quentin Blake’s stunning artwork – The Box of Delights and its sequel The Midnight Folk are a must-read for any child. A genuine fantasy classic in the tradition of Peter Pan, Alice's Adventures in Wonderland or The Wonderful Wizard of Oz. A wonderful book for early readers aged 8 and up.

Can this be the Time Warp Trio series by Jon Scieszka, whose first book is Knights of the Kitchen Table?

My memory is also fuzzy, but I think I read about three books in the series.

These books are:

• a series
• published from 1991 to 2006
• involving three boys (but not siblings)
• who travel back in time using a book (always called "The Book")
• and a magician uncle who gives The Book to the main character

I don't know about an old house, or turning into animals. I know that the first book is in King Arthur's time, and other Arthurian stories involve Merlin turning Arthur into animals, so maybe that was in there.

Sounds like the Narnia series: a series of 7 novels for children by the English author C S Lewis, published between 1950 and 1956.

In the initial novel, The Lion, the Witch and the Wardrobe, four children (three of whom are brother and sisters) go on holiday to an old house, where they travel through a magic wardrobe into the land of Narnia. The Witch who they encounter there puts a spell on one of the boys, turning him into an animal.

In the subsequent books, they keep going back to Narnia through the wardrobe (or sometimes without even using the wardrobe). The witch in the first book is succeeded in one of the sequels, entitled The Magician's Nephew, by a wizard (and his nephew) -- who live in the house in that story only.

There is a time travel element to the stories, in that time passes at a different rate in Narnia, such that however long the children spend there, no time has passed in England. And every time they visit Narnia a great deal of time has passed there - centuries perhaps - even though only a few months have passed in England.

Narnia is populated by lots of talking animals (including a talking horse in one book, The Horse and His Boy), so that there are a lot of other animals in the tales, in addition to the children occasionally being turned into animals.