Please send old photos of children at neighborhood swimming pools, within the next week, to Way Back When, Sun Magazine, 501 N. Calvert St., Baltimore, Md. 21278. You must include caption information and your daytime phone number. Also, enclose a stamped, self-addressed envelope if you'd like your photo returned. If your photo is your only copy, please send a good-quality duplicate, not the original. No faxes or newspaper clippings, please.