BY DAY Skip Larson is a retired National Park Service manager and set designer; Milton Shomo, a senior network engineer; and Ian Smith Dewaal, a senior counsel for the Department of Justice. But for a month of Saturdays and Sundays, beginning as early as mid-October and culminating during the intense December holiday season, these men don dance shoes and become Nutcracker dads. Sure, they're real-life dads, but Nutcracker fatherhood is a rarefied experience of another sort.