It is probably fair to say that most young readers' first experience of 'Stuart Little' will be through the two films based loosely on this book. As such, they might expect a lively, funny, fast-paced plot with plenty of action and humor. However, 'Stuart Little' was first published in 1945, and styles of humor and standards of children's books have certainly altered over the years.
Stuart was created by E B White, co-author of that well-known writer's bible 'Strunk & White's Elements of Style' - so readers might rightly expect a flawlessly written tale. Perhaps it was back in 1945. However, good punctuation and grammar are all very well - but pacing and plot are basic requirements too. What you do get, by today's standards, is something flawlessly dull. The humor is wry, gentle, whimsical, and in its way quite charming, but to be perfectly honest, if it were offered to a publisher today, it would most likely be returned with a polite note of rejection.
Many in the USA view this as something of a classic, the American equivalent of 'Winnie the Pooh' - but this is wishful thinking. Whereas 'Pooh' continues to enchant countless new readers, Stuart is perhaps best sticking to his cinematic outings for the young. E B White also wrote Charlotte's web, though this has weathered the passing of time considerably better.
No doubt many older American readers who have fond childhood memories of this book will strongly disagree, but if you are planning on buying this book for a young UK reader, then you may fair better with something more contemporary. If you like tales about mice - why not check out 'Time Stops for No Mouse,' by Michael Hoeye - the first in the Hermux Tantamoq adventures