  Children's cognitive abilities are sometimes cited as AI benchmarks. How can
the most common 1,000 concepts (89\% of everyday use) be learnt in a
naturalistic children's setting? Cognitive development in children is about
quality, and new concepts can be conveyed via simple examples. Our approach of
knowledge scaffolding uses simple objects and actions to convey concepts, like
how children are taught. We introduce ABCDE, an interactive 3D environment
modeled after a typical playroom for children. It comes with 300+ unique 3D
object assets (mostly toys), and a large action space for child and parent
agents to interact with objects and each other. ABCDE is the first environment
aimed at mimicking a naturalistic setting for cognitive development in
children; no other environment focuses on high-level concept learning through
learner-teacher interactions. The simulator can be found at
https://pypi.org/project/ABCDESim/1.0.0/
