The authors of the charming little off-Broadway musical The Fantasticks followed up with I Do! I Do!, a charming little musical given the Broadway treatment in 1965, even though it has only two characters, Agnes and Michael, whom we track through 50 years of marriage (1895-1945). If you had Mary Martin and Robert Preston as your stars, you’d put it on Broadway, too. But I Do! I Do! really is a chamber musical comedy, as this loving new production at American Theater Company warmly confirms. It’s updated to Chicago, 1957-2007, with the 1950s being the latest one might reliably expect a virginal bride. Heidi Kettenring and Stef Tovar star. American Theater Company, 1909 W. Byron, through Nov. 4; 773-929-1031; $30-$35. Photo by Johnny Knight