We study how reinforcement learning algorithms and children develop their causal curriculum to achieve a challenging goal that is not solvable at first. Adopting the Procgen environments that comprise various tasks as challenging goals, we found that 5- to 7-year-old children actively used their current level progress to determine their next step in the curriculum and made improvements to solving the goal during this process. This suggests that children treat their level progress as an intrinsic reward, and are motivated to master easier levels in order to do better at the more difficult one, even without explicit reward. To evaluate RL agents, we exposed them to the same demanding Procgen environments as children and employed several curriculum learning methodologies. Our results demonstrate that RL agents that emulate children by incorporating level progress as an intrinsic reward signal exhibit greater stability and are more likely to converge during training, compared to RL agents solely reliant on extrinsic reward signals for game-solving. Curriculum learning may also offer a significant reduction in the number of frames needed to solve a target environment. Taken together, our human-inspired findings suggest a potential path forward for addressing catastrophic forgetting or domain shift during curriculum learning in RL agents.