From maps sketched in sand to supercomputing software, humans ubiquitously enhance cognitive performance by creating and using artifacts that bear mental load [1, 2, 3, 4, 5]. This extension of information processing into the environment has taken center stage in debates about the nature of cognition in humans and other animals [6, 7, 8, 9]. How does the human mind acquire such strategies? In two experiments, we investigated the developmental origins of cognitive offloading in 150 children aged between 4 and 11 years. We created a memory task in which children were required to recall the location of hidden targets. In one experiment, participants were provided with a pre-specified cognitive offloading opportunity: an option to mark the target locations with tokens during the hiding period. Even 4-year-old children quickly adopted this external strategy and, in line with a metacognitive account, children across ages offloaded more often when the task was more difficult. In a second experiment, we provided children with the means to devise their own cognitive offloading strategy. Very few younger children spontaneously devised a solution, but by ages 10 and 11, nearly all did so. In a follow-up test phase, a simple prompt greatly increased the rate at which the younger children devised an offloading strategy. These findings suggest that sensitivity to the difficulties of thinking arises early in development and improves throughout the early school years, with children learning to modify the world around them to compensate for their cognitive limits.