I want to ask my child what font to learn when learning calligraphy in primary school. Official script? Or regular script? There are those calligraphy masters who use regular script.

Official script is better, there is no need to learn regular script. There are many people who learn official script and regular script. If you want to use seal script, it can be divided into big seal script and small seal script, both of which are used before and after Qin dynasty, which are more complicated. People nowadays basically don't understand it. Children are not advised to learn this, which is easy to be confused with modern Chinese characters. However, few people learn seal script.