Background: Arterial cannulation in young children can be challenging. Ultrasound guidance using focused acoustic shadowing may be suitable for guiding radial artery puncture in young children. The present research tested the hypothesis that ultrasound guidance using focused acoustic shadowing helps increase the success rate of radial artery cannulation in this population. Methods: In a double-blinded, parallel-group trial, 79 young children undergoing surgery under general anesthesia were randomly assigned to two groups (1:1 ratio): the traditional ultrasound group and the novel ultrasound group. Young children in the traditional group underwent conventional ultrasound-guided radial artery puncture, whereas those in the novel ultrasound group underwent radial artery puncture guided by acoustic shadowing ultrasound with double developing lines. All radial artery punctures were performed using the short-axis out-of-plane approach. The primary endpoint was the success rate of cannulation at the first attempt. The secondary endpoints included cannulation failure rate, ultrasound location time, and puncture time. Results: The success rate of cannulation at the first attempt in the novel ultrasound group (35 of 39 [90%]) was significantly higher than that in the traditional ultrasound group (24 of 40 [60%]; difference: 30% [95% CI, 12 to 48%], P = 0.002). None of the patients in the ultrasound with acoustic shadowing group experienced failure of radial artery puncture and cannulation. The ultrasound location time and puncture time in the ultrasound acoustic shadowing group were significantly lower than that in the traditional ultrasound group (location time: median [interquartile range]: 6 [5, 8] vs. 18 [15, 21] s; puncture time: 24 [15, 41] vs. 40 [23, 56] s). Conclusions: Acoustic shadowing via the use of double developing lines significantly improved the success rate of radial artery puncture in young children, compared with that achieved with the use of traditional ultrasound guidance.