Children lack awareness and understanding of their rights and the law. There is a need to address this gap and empower children to become advocates for their rights when they encounter law-related issues. A promising approach to achieving this is through the use of games. In particular, games focused on learning have evolved into novel tools that can raise awareness as well as help children acquire essential skills. In this paper, we present a child-centred design approach to evaluating the initial version of a learning game designed to help children across a wide age range (3-15 years) and with diverse characteristics, improve their legal knowledge, skills, and confidence. This study supports the integral role and value of child participation in testing the usability of a law-based learning game and shaping its design. A mixed methods approach, grounded in user-centred principles, was employed to assess the first prototype (P1) of the game. 45 children from various schools and early years settings in South Yorkshire and the Midlands, UK were involved. This included children from: 1) advisory groups, 2) case study groups, and 3) game development groups, with an age range of 4 to 16 years old. School staff were also invited to give their feedback. Quantitative and qualitative data were gathered through questionnaires, and field note observations, and analyses were conducted through both thematic analysis and non-parametric statistical methods. We found the game was received positively overall, but further development was needed to make it accessible and engaging, especially for the youngest participants. Importantly, participants of diverse ages and characteristics shared valuable insights into enhancements to make the game more intuitive, interactive, and enjoyable, and these findings informed the development of the beta version of the game.