Introduction & Note on the Nature of the Question

This question is a bit half-and-half with historical and philosophical/psychological, so I'll do my best to give an answer to the historical question--did Rousseau leave his kids to a foundling hospital (and why)--and touch on the second question of "why did he write an educational treatise" from, naturally, a more subjective point of view.

I do wish to start with the second, though, because it's a logical fallacy to claim someone's personal inadequacies prevents them from being able to speak to a topic on an abstract or theoretical level. Many philosophers have written on subjects such as education without having actually "tested" their theories in reality; more specifically, the idea that you have to be a good parent to be able to write about education is highly contestable. Therefore the claim that Rousseau's personal history with his children precludes him from speaking to human nature with regards to childhood education remains an ad hominem attack, versus an actual critique of his educational works. We have no way of knowing the personal merits or failings of every writer as a parent. Even if we did, such details could only ever allow us to "judge" the person, not the work. So it is with Rousseau.

Rousseau & his Children: Yes, he did give them up to a Foundling Hospital

Now, that being said, onto the history! It is true that at his request (and with the reluctant approval of the children's mother) the 5 children he sired were taken to a foundling center directly after their birth by a midwife. I think it's important straight away to consider the climate of a culture removed from us by 250+ years. It was far more common in the days of limited methods of contraception & abortion to take unwanted children to a foundling hospital, particularly when the couple was unmarried (as were Rousseau & Thérèse) or financially indigent or unstable (as they often were).

Rousseau's actions were still looked down upon by contemporaries, though criticisms mainly came from intellectual rivals wishing to throw witty barbs rather than a concerted moral opposition. Rousseau himself seemed to vaciliate for most of his life about his decision: he expressed deep regret in certain letters, even citing his abstract attachment as his motivation for writing Emile, his widly successful treatise on education. Yet we can not take his regrets as a desire to have done actions differently, as this remorse predates the birth of his last children.

Another aspect of the affiar, and perhaps the more reprehensible, is his admission that Thérèse did not wish to give up her children; instead, she was persuaded to do so by Rousseau, whose attitude towards Thérèse in his writings makes it very clear that he did not love her in a romantic way, nor did he value her much as a companion. She was sort of just "there" whenever Rousseau wished her to be. While it is possible that toward the end of his life he appreciated her more, he never would write about her with the adulation he bestowed upon other women.

Why did Rousseau give up his children?

The "million dollar question," then, that everyone from psychologists to historians have tried to crack: Why did Rousseau abandon his children? In short, Rousseau's reasons for asking Thérèse to give up their children were part practical--they were unmarried, poor, and Rousseau was generally on-the-move due to running into censorship issues; and part personal--Rousseau did not feel himself up to the task, nor did he want the responsibility, of children.

Taking Rousseau as our main source, as well as some contextual clues from those around him, I would offer up three main reasons, given by what I believe is their order of importance. First was Rousseau's personal disinclination for parental responsibility & his personal characteristics; second was his views on "ideal" child-rearing; thid on the situation of he & Thérèse and cultural norms.

First: Rousseau's Personal Reasons

First, Rousseau often intimates in his writings--particularly his Confessions--that he did not believe himself up to the task personally of raising children, who were a responsibility too difficult to bear. Rousseau was incredibly sensitive, prone to vacilate between pride and self-deprecation; capable of taking minor set-backs as crushing failures; impetuous, impatient, and entirely unwilling or unable to settle in one place for too long--in short, Rousseau likely feared parenthood as much as he knew he was not up for the job.

To a person who was alternately seized with inspiration, working sequestered for long stretches of time, and who was continually moving about due to persecution, towing children would have been highly inconvinient, and the decision certainly was made for selfish reasons: Rousseau valued his own career, his own person, and his own happiness, over that of his potential offspring. On another note, Rousseau constantly tells us how draining he found the presence of others, and how much he valued time alone. Moreover, Rousseau intimates that fairly commonplace situations gave him a great deal of anxiety, and he was an obsessive worrier. In all, Rousseau as a person had many traits that would have made being a parent an unbearable strain on his mental health.

Second: Rousseau's Vision of a "Perfect" Society

The second "reason" was that Rousseau believed in state-run communal education--think Sparta. Boys and girls should be taken from their parents, who could only instill them with the same self-centered morals they had; this cylce had led to a bunch of individuals scattered throughout a nation, rather than a group of Citizens with a love for their state and for one another. Now, under no pretenses did Rousseau honestly believe that the foundling hospitals of France were some miniature lyceums. This "point" seems to rise up not as a "justification" so much as an apologia, as though he's trying to assuage his own guilt more than convince his reader. While there was something of Rousseau's personality here--he believed he would be a poor caregiver--there is no doubt that Rousseau's views on a perfect education likely served to "justify" his decision in his darkest periods of regret.

Thid: Rousseau's Relationship with the Children's mother

Third, Rousseau's mistress, Thérèse Levasseur. I really already mentioned this above, but to drive it home in the most blunt way possible: Rousseau did not want to marry Thérèse (though he eventually did marry her unofficially late in life, & she was the inheritor of his estate) and he really did not want to be tied to her by anything as permanent as children. Rousseau lived a "romantic" life, wandering alongside his imagination, and taking up with some of the most high-ranking women of the day. Thérèse, a laundress from a poor family in Paris, whom he describes as neither beautiful, nor intelligent, nor really anything other than a constant, dependable presence, severely clashed with the "other" life Rousseau led.

(contd. in following comment)