It is surprising to me that there does not seem to be any English textbooks on the life of Prince Siddhartha in general.
Such information is unlikely to be in the suttas, but could be in the Vinaya Piṭaka. I have not had time to look at the Vinaya Piṭaka (I only started reading suttas after the Parinibbana of Waharaka Thero; until then I just relied on his desanas).
When I was growing up in Sri Lanka, these details on Buddha’s life before Enlightenment (i.e., Prince Siddhartha’s) were taught in school. There were books written in Sinhala. So, it never occurred me to even look into this aspect all this time.
After seeing upekkha100’s post, I looked into it a bit, but could not find much online or in textbook form.
If anyone knows any text books or online info, that would be very beneficial.