Unity - The multiplatform game creation tools for everyone.
Etoys - Etoys is an educational tool for teaching children powerful ideas in compelling ways.
Godot Engine - Feature-packed 2D and 3D open source game engine.
GCompris - Educational Game for Children 2 to 10 years old.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
childsplay - Childsplay is a collection of educational activities for young children and runs on Windows, OSX, and Linux. Childsplay can be used at home, kindergartens and pre-schools.