When Siddhārtha Gautama left his home to become an ascetic, he left a wife, son, father and step mother. His achievement of enlightenment and subsequent teachings of the 4 Noble Truths and 8 Fold Noble Path has brought obvious benefit to the world for the potential of the cessation of suffering. But what is known about the suffering of the Buddha's personal family due to his leaving? As the Buddha, did he ever speak of this matter?
The Buddha praised princess Yashodara's virtue by dispensing the Channakinnara Jataka when he visited her at Kapilavatthu. Yashodara has never been a wife to another man since the life when Bodhisatva received the confirmation from Deepankara Buddha to become a Buddha in the future. The Bodhisatva was always her husband.
So the Bodhisatva and his family have spent plenty of time together as family in many a previous life. If that didn't take away their suffering, what's the point of doing more of the same?
Lets take an analogy. If your family is suffering from a mortal illness and if you alone have the capability to go find the cure, wouldn't you leave them behind to get the cure instead of lingering there to give them false comfort?
Are you familiar with the Vessantara-jātaka? As the last tale in the Jataka series, it is basically the story of the Buddha’s incarnation immediately preceding his life as Shakyamuni (so you could say it’s rather significant!) Be that as it may, what happens to the Buddha-figure's immediate family is rather shocking.
The Vessantara-jātaka is supposed to illustrate the virtue of dāna, or generosity. The main character is a prince who goes into the forest (in effect becomes a renunciant) in order to save his father’s kingdom. His wife and two children go with him. At one point an old Brahmin whose wife needs a personal slave comes to Vessantara and asks him to give up his children, and he does. Later he also gives away his wife, but luckily it is the god Sakka who receives her. Later everything is reversed, Vessantara becomes king and riches rain down on his palace from the sky, so he is able to practice the dana virtue in an unlimited way.
This Jataka has a prominent place in Thai Buddhism – everyone knows the story, it was used for teaching and is often recited at temples as an exercise in merit-making. Charles Keyes wrote that it was historically one of three core texts in Thai popular Buddhist practice, along with the Traiphum, a work of cosmology, and the story of Phra Malai, which contains a lesson about the future Buddha Maitreya. (By the way, neither of the latter texts appears in the Tripitaka at all.)
Many Thais are disturbed about the seemingly anti-family message of the Vessantara-jātaka. (Other, less well-known jatakas can be disturbing too. There is one where a male hermit lets his female companion, also a renunciant, starve to death – she is just too weak to follow the path.)
It’s all about ridding oneself of attachments, of course. One of the most difficult things about becoming a monk must be to do this, although in practice the severing of ties is not absolute – family members may continue to feed the monk by donating food on his morning rounds, for instance. The Vessantara-jātaka has a message for both laypeople (how virtuous it is to give) and for monks (a model for renouncing worldly ties.) That may account for its popularity - who knows really?
Here’s a good summary of the Vessantara story – the full version is very long.
The suffering his family experienced at his departure was only because of their attachments. They were in the royal family; he knew they would be taken care of materially.
The Buddha's son became a monk under the Buddha and his ex-wife became the first nun. His father convinced the Buddha to make a rule for monks that a person couldn't become a monk or a nun without the permission of their parents (if living) and their spouse (if married.) Indeed, it was the rule that required the permission of both parents that prevented me from becoming a monk, though I cannot guarantee that it would have happened even with their permission.
On a related note, according to the Commentaries (?), the entire Sakya clan was massacred during the Buddha's lifetime. (See, for example, http://www.palikanon.com/english/pali_names/sa/sakya.htm)