Blushing has adaptive social functions. However, blushing is also assumed to be a hallmark of social anxiety and shyness. For the first time, blushing and its relation to the expressions of shyness and social anxiety was examined in early childhood. Four-and-a-half-year-old children (N = 102) were asked to perform (singing in front of an audience) and watched back their performance in the presence of that audience. Physiological blushing (blood volume pulse, blood volume, and cheek temperature) was measured, and positive (gaze and/or head aversion with smiling) and negative expressions of shyness (gaze and/or head aversion with negative facial expressions) were observed. In addition, both parents reported their child’s social anxiety level. A higher level of blushing response was related to greater social anxiety in children who displayed few positive shy expressions, but not in children who displayed many positive shy expressions during the performance. Moreover, children who expressed many negative shy expressions were highly socially anxious, no matter their blushing. Our findings suggest that blushing appears to be an early indicator of social anxiety in children who are not able to successfully cope with fearful social situations. In contrast, blushing, in combination with positive shy behaviors, appears to be an adaptive social mechanism that may protect from heightened social anxiety.