Now We Are Six, by A.A. Milne, illustrated by Ernest Shephard, Dutton Children's Book, originally published in 1927.
I love this book.
When I was six, my great-aunt (whom I loved very much) gave me a copy of this book for my birthday. Over the years, that copy was lost, but not before it was practically read to death. I didn't remember any specific poems in this, but I've always remembered that I loved it.
Last week, my son, Thomas, turned six. I gave him this book for his birthday. Later that evening we read from it, and how perfect was it that we read about Sir Thomas Tom. I didn't remember Sir Thomas Tom, but there is a good chance that my son will when he gets older.