Managing negative emotion can be challenging for autistic individuals and their families from a young age. Parents help young children manage negative emotions by responding in comforting or supportive ways. Not much research has examined how negative emotions and parent responses to negative emotions are different in very young autistic children. This study used videotapes of 18-month-old toddlers and parents at home. We examined how much and how intensely toddlers expressed negative emotion in everyday situations, and how parents responded. Participants were younger siblings of autistic children, and we compared three groups-children that (1) later received an autism diagnosis; (2) had language delays but not autism; and (3) had no delays or autism. We found that autistic toddlers' negative emotion was more likely to be intense and to continue once it started compared with children without delays or autism. Language-delayed toddlers also showed some, but not all these differences. Parents responded similarly to negative emotions in all groups. When parents used strategies to help, it reduced the chances of the negative emotions continuing, although it may have been less helpful for autistic toddlers. This study shows that autistic children may express more intense and long-lasting negative emotions from an early age. It also shows that parents of autistic children are very responsive to their children's negative emotions, but these responses may not be as helpful to autistic children. While more research is needed, this study helps us understand how autistic toddlers may express and experience emotions differently.