Personalized Math Rocks Newborn Layette. Math rocks with three happy rocks dancing with numbers is a humorous design for mathematicians, students and teachers at birthdays, holidays, back to school and graduation. 100% combed ringspun cotton 5.8 ounce 1×1 baby rib sleeper. 3/8" flatlock binding at envelope neck and cuffs. Back sleeve flap to protect hands. Elastic opening at bottom. Infant: 0-3 Months