The aim of this study was to investigate, describe and understand the developmental function (musical and social/emotional) of nine toddlers’ private spontaneous songs. Between the initial interviews with the eight families and follow-up interviews 5 to 6 weeks later, parents observed their child at home twice a week for 4 consecutive weeks. When the child was alone at bedtime, the parents stood outside the bedroom door and completed a written Parent’s Observation and Reflection Form (PORF) describing and contextualizing what they heard on a minute-by-minute basis for the first 15 minutes of each session. Additionally, the parents collected audio recordings of the eight sessions using a smartphone that they placed inside the child’s room. Data sources included transcripts from family interviews, field notes, PORFs, and audio recordings. Findings suggest that many of the toddlers used solitary spontaneous singing at bedtime as a way to demonstrate and practice musical skill, reflect, experiment, self-soothe, and understand their own worlds. Spontaneous singing functioned to support these adaptive strategies during this intense developmental period. Further research is needed to understand the conditions and varieties of toddlers’ private spontaneous crib song.