We're going to make a new math course for kids as intermediary between middle and high school with math profile (for preparation to entrance exams to high school), and before the main part (arithmetic, addition, multiplication, Minkowski addition, Fundamental theorem of arithmetic with proofs) we'd like to put some content about proofs tactics, how to proof theorems, formal logic and basic terms like ring, field, group, etc.
What would you recommend to look at among introductory courses as a preparation material to such classes?
I understand that it sounds like a broad question, but I'was trying to look through some materials like Coursera's "Mathematical thinking" and it seems not to be enough for this goal. Can you help me with collection of materials for kids, which are ready to take and systemized?
Thank you all!