It is suggested to start with regular script. The reason for this is the following：
Regular script is more practical than seal script and official script, and is widely used in learning and writing.
Now primary school students are required to write standardized characters, that is, regular script, which is more in line with the current learning requirements.
Seal script is more difficult to identify than regular script, and regular script writing is easy to be recognized by people around (classmates and teachers), which can greatly improve children's self-confidence in study and life.
My humble opinion, I hope I can help you.