Kipling has, justifiably on the whole, a reputation for being the Poet Laureate of the British Empire, from which his work has suffered, particularly in these postcolonial times. Stalky & Co is no exception - it was written with the view of encouraging more 'stalky' (a bending-the-rules-type cunning) boys to join up to the British Army after the humiliating defeat of the Boer War.
Don't let this put you off however. Kipling is far more ambivalent concerning the Empire than most people think, and this comes across in the book's darker passages. Aimed at teenage boys (not little kids), the three main characters of Stalky, M'Turk and Beetle (an autobiographical incarnation) get up to traditional public school 'high jinks' and larks, but also some rather morally questionable activities too. The reader gets swept up in the irresistable sense of fun, camaraderie and not a little schadenfreude, then gets stranded, asking themselves whether the pranks they've enjoyed are strictly acceptable. But the feeling you're left with is a deeply satisfying one of watching the geeky, unpopular underdogs getting one over on the arrogant big boys.
Enjoy it and savour the nastiness of public school as well as its idyllic side!