Mayo Clinic and the American Journal of Public Health advise that above 120 degrees Fahrenheit, hot water can scald in a short enough exposure time to be a significant risk, especially for children, who have thinner skin. Scalding is a factor of both temperature and time of exposure.
At 130 degrees Fahrenheit, hot water can cause second degree burns in under five minutes and in as little as 20 seconds, depending on conditions, according to Accurate Building Inspectors. Above 150 degrees, it can cause second-degree or third-degree burns, essentially on contact. Liquids that might come in contact with skin should be kept under 120 degrees and ideally closer to 100 degrees, especially around young children.