Baby strollers can be incompatible with city life, requiring strength, stamina, and a fleet of specialized carriages and carriers to contend with hills, cobblestones, and, in winter, mounds of snow. But now this problem for urban parents has caught the attention of a team of students from Massachusetts Institute of Technology and the Rhode Island School of Design. They believe they have created a way to help city parents get around more efficiently, building a stroller and harness system called BuzzyBaby.