For non-fictional diaries, your own school library will probably not offer much beyond The Diary of Anne Frank and extracts from Pepys. But by going to your public library and into cyberspace, you will find a wealth of material suitable for primary children.
Starting with a Victorian diarist, William Allingham's diary for 1866 contains a description of a visit to the Tennysons, during which the poet is complaining of uncomfortable boots which he paid pound;2 12s 6d in the Burlington Arcade - an example of the way in which diaries can teach us that small discomforts and annoyances are universal. Moving on a bit, you might not think Virginia Woolf a likely source of material for primary children, but if we want to advocate diary-keeping as an excellent means of flexing the writing muscle, then Woolf's entry for April 19 1920 in which she talks of her belief "that the habit of writing thus for my own eye only is good practice. It loosens the ligaments" is instructive.
For more contemporary examples I would turn to sport or endurance, and look perhaps for a cricketer's account of an overseas tour, or an arctic explorer's journal.
Undoubtedly the richest collection of diaries and the one most instantly accessible is online. Casting a critical eye down the results of a random search should have you locating interesting material in minutes. It only took me a moment to stumble on www.alittlehistory.comDi-begin.htm, a diary kept by a 10-year-old boy in 1954 in a small American town.
A Diary 1824-1889, William Allingham (Penguin) and The Diary of Virginia Woolf, Volume 1 1915-19 (Penguin) can both be found second-hand and in libraries
A Pepys diary weblog, with a new entry appearing each day, is on www.pepysdiary.com
Contemporary UK working-life online
Two extracts from before and during the American Civil
Online diary by 2nd grade American