The most important thing for children to learn calligraphy is to cultivate their interest in calligraphy. You spend so much energy on your child now, but if you don't cultivate your interest in calligraphy, it is unknown whether he will learn/write a good hand in the future ... even if you don't have to worry/your child is old, he will try his best to practice calligraphy. For example, when I was 15 years old, I found such a wonderful thing as calligraphy. After I became interested, I went to the teacher to learn.
You are right to paint the child red. Nowadays, most calligraphy classes teach children to paint red and begin to transition to temporary posts. I suggest you not to enlarge the copybook, because different glyphs have different strokes. Ancient calligraphers have long said this question: "Different glyphs make different strokes."
If you really don't know anything, you'd better consult someone who knows calligraphy first, or study the introduction theory of calligraphy yourself before teaching your children. Again, children should learn to be correct if they don't learn. I suggest you talk to the calligraphy teacher directly. Even if they don't accept your children, they should tell you how to teach yourself at home. Online answers really can't give you a satisfactory answer. I hope it can help a little.