Co-thought gestures are understudied as compared to co-speech gestures yet, may provide insight into cognitive functions of gestures that are independent of speech processes. A recent study with adults showed that co-thought gesticulation occurred spontaneously during mental preparation of problem solving. Moreover, co-thought gesturing (either spontaneous or instructed) during mental preparation was effective for subsequent solving of the Tower of Hanoi under conditions of high cognitive load (i.e., when visual working memory capacity was limited and when the task was more difficult). In this preregistered study (https://osf.io/dreks/), we investigated whether co-thought gestures would also spontaneously occur and would aid problem-solving processes in children (N = 74; 8-12 years old) under high load conditions. Although children also spontaneously used co-thought gestures during mental problem solving, this did not aid their subsequent performance when physically solving the problem. If these null results are on track, co-thought gesture effects may be different in adults and children.