I now also have a copy of the 4th Robin birthday book and birthday postcard...as they came from the same child who received the 3rd birthday book I know that this postcard was sent a year later and presumably ties in with her next (i.e. 4th) birthday.
The book is very similar to the 3rd birthday book (soft cover, slightly larger than a paperback and is 12 pages long) and I can't believe that it would have lasted very long in the hands of the average 4 year old!
Inside it's a mixture of poems, puzzles, (very) short stories and a couple of comic strips - in this case Andy Pandy and The story of Woppit. All of which is perhaps indicative of a book for a four year-old.
As a nod to friend of the blog Steve Hollands I include here the Woppit story as he wrote all about Woppit here on Bear Alley