Interest in science is critical for science learning. The family plays a major role in supporting the development of children's interest in science by eliciting and fostering interest and engagement with science content and practice. This study characterizes triggers for interest in science in everyday family life and measures the duration of resulting engagement manifesting situational interest. In an insider researcher-ethnography of one family, we collected video and audio recordings of science-related interactions using fixed 24/7 audio and video cameras in the house and Go-Pro cameras outdoors. We identified 397 science interest-triggering events and classified them along three dimensions: (1) the connection between the stimulus and the object of interest (direct, indirect, or unidentified); (2) the design of the stimulus (designed or undesigned); (3) the attention to the stimulus (self-noticed or mediated). We found most triggers were direct (87%) and undesigned (82%), and they were equally mediated and self-noticed (50%-50%). Moreover, although designed triggers were relatively rare, they elicited longer situational interest than undesigned triggers. Interaction analysis of two illustrative events showed that this difference was related not only to features of the trigger design but also to the way participants co-constructed the interaction around it. The study's findings underscore the significance of developing targeted triggers for science learning in family contexts and providing parents with practical strategies to leverage undesigned triggers.