For weary parents rolling up their sleeves for around-the-clock diaper duty, a bill with bipartisan support in Kentucky would deliver tax relief when purchasing a necessity that adds up to a hefty expense. The measure would exempt diapers from the state’s 6% sales tax. Senators from both parties have signed on as cosponsors, and the proposal received a hearty endorsement from the operator of a Kentucky diaper bank who says it goes to the heart of a harsh reality for some struggling families — cutting back on food and other expenses to keep their infants in fresh diapers or reusing disposable diapers.