After reading with your child portions from the brochure The Origin of Life ​ — Five Questions Worth Asking, you could ask what arguments he finds most thought provoking.
أَوْضِحْ لِوَلَدِكَ أَنَّهُ يَسْتَطِيعُ أَنْ يَتْبَعَ ٱلْخُطُوَاتِ نَفْسَهَا عِنْدَ ٱلتَّحَدُّثِ إِلَى رَفِيقِهِ .‏