Observations of young children are conducted in an educational setting by practitioners to plan and assess activities based on the individual development and needs of the child. Challenges include: recording, how to be an observer rather than a participant, and connecting developmental theory to observable behaviour.Several projects have simulated children in their learning environments, aimed mainly at pre-service teachers, but these have neither been for young children where the activity is play-based nor where the adult is supportive of the child's interests. Some simulations have used 3D graphics to represent a child via a role-playing adult but there have been few attempts to use autonomous characters.A novel real-time interactive 3D graphical simulation-Observation-was developed, providing a physical sandbox for users to: add autonomous characters (representing children), add objects, and customise the play-based environment. The definitions of the characters were informed by the findings from early childhood research. The simulation was evaluated using two complementary serious game frameworks and its utility was evaluated by professionals within the field of early childhood education comprising university students and educators, and local education authority advisors. An explorative, mixed methods approach was taken, triangulating across: a pilot study and a main study; different research instruments (simulation activity plus questionnaire, focus groups, interviews); and a range of participants. The simulation has utility because: it is an interesting way to explore the behaviours of young children, the theoretical understanding behind children's play can be deepened, and observational skills can be developed. The simulation has wide appeal because the perceived utility of the simulation is not influenced by: professional experience, number of real-life observations of young children, or time spent playing video games. Age is considered to be the most important omission from the abstract character in the simulation.