Sources begins:

Exploring Mathematics

This enables accessing material relating to two things: a) school mathematics, and b) sustaining/initiating interest in quantity and shape. The items vary in level, but at least their beginnings should be understandable.

Books begins:

Reasoning About Quantity

About Mathematics - Book Sources and Quotations

Mathematics is interesting ... and sometimes difficult. But it isn't what we think it is. The mathematician Sonya Kovalevsky wrote "many who have never had the occasion to discover more about mathematics, confuse it with arithmetic and consider it a dry and arid science. In reality, however, it is a science which demands the greatest imagination.