Reddit reviews Mathematics for Elementary Teachers: A Conceptual Approach

So I might actually suggest a 'math for elementary teachers' book for yourself (alternate here), so that you can get an idea of how to approach these kinds of problems with visual aids, such as what kinds of ways you can draw pictures of long division, etc. In other words, most people don't use textbooks with 4th/5th graders, but a lot of worksheets and packets, with activities and explorations drawn from curricula like this.