According to piaget, which ability do children gain during middle childhood?

According to Jean Piaget, children in middle childhood experience an increase in their ability to solve concrete problems. They grow in terms of their comprehension of abstract concepts around mathematics. They also gain the ability to understand causal relationships between things (cause and effect), and the ability to weigh objects in their head without being thrown off by the sizes / shapes of things.

The one that most represents the earths mantle would be the skin since the mantle is the upper part of the earths depths which is just like the skin of an apple.