If you're 12 or under, you are invited to send in your poems, drawings, and short stories on any subject you choose. We'd also like to hear about the books you read, movies you see, or school projects and class trips you have enjoyed. And we're interested in good photos you've taken of your friends, families, and pets. This is your page -- a place where you can show what discoveries you've made in your world. We can't use everything we receive, but we'll return unused items if you include a stamped, self-addressed envelope. Send to Children's Page, The Christian Science Monitor, One Norway Street, Boston, Mass. 02115.