On the day before what would have been Freddie Mercury's 68th birthday, the all-female Queen tribute band Gunpowder Gelatine brought a bit of bombast to the normally quiet lawn of the Loring-Greenough House. The group performed arena-rock classics like "Bohemian Rhapsody," "We Will Rock You" and "Fat Bottomed Girls" on a small stretch of grass hemmed in by trees. Children wandered in and out of the stage area and parents carrying kids or pushing strollers passed right in front of the performers. Singer Bethany Hanley probably won points with parents by dropping some of Queen's more violent lyrics in deference to the number of toddlers in the audience. The Boston-based group plays regular gigs at spots like the Midway and Johnny D's, said keyboardist Kate Dobroth.