This is more Charles experimentation with words. In this exercise, Charles writes a letter, makes Dad think of a word that starts with the letter, followed by Dad spelling out the word so Charles can write it down. That accounts for the “ICKY” “HOT” “SOUP”, “OX”, and “FROG”.
However, Charles wrote “POI” all by himself. Charles had no idea what it meant, but he was very happy to have written a word.
But the most important part of this is the highlighted part. Charles wrote that without any sort of prompting from Dad. Dad is so proud! [sniff]