child, young of animals
兒 centers on a young being: a child or the young of animals. It captures the idea of offspring or juvenile stage.
兒 is the traditional form of 児. It originally depicted a child with an open fontanel on top, represented by 臼, and legs below, represented by 儿. The modern simplified form 児 replaces the top with a simpler shape.
The top 臼 looks like a baby's soft head with an open fontanel, and the bottom 儿 looks like little legs. Together they form a child.
For ジ, imagine a child saying 'Gee!' in excitement: Gee -> ジ, and the child is the young one.