Ultrasonography (US) is a useful screening method for the diagnosis of developmental dysplasia of the hip (DDH) and congenital spinal anomalies in infants. In addition, US is a useful, noninvasive imaging modality for the diagnosis of transient synovitis in children. The early detection of DDH leads to a better prognosis without surgical intervention. Moreover, spinal US allows the detection of congenital malformations and can also demonstrate normal anatomy and normal variants that may resemble disorders. Therefore, radiologists should be familiar with the sonographic anatomy of the normal infant hip, scanning and measurement techniques for DDH, the US features of transient synovitis in children, spinal US techniques, and the US features of normal anatomical structures, normal variants, and congenital spinal anomalies.