I'm asking this because while reading the Stanford Encyclopedia of Philosophy article on Rousseau, I was struck by the following passage:
In 1745 Rousseau met Thérèse Levasseur, a barely literate laundry-maid who became his lover and, later, his wife. According to Rousseau’s own account, Thérèse bore him five children, all of whom were deposited at the foundling hospital shortly after birth, an almost certain sentence of death in eighteenth-century France. Rousseau’s abandonment of his children was later to be used against him by Voltaire.
I highlighted the relevant sentence. Is the claim true?
The SEP article lists a bibliography at the end and maybe some of them contains the citation for the claim, but I don't have the capacity to research this question further.
According to search, previously Rousseau's children have been discussed here on AskHistorians, but only from the angle "how common it was", not "what happened to the kids later".
According to Laurence L. Bongie, in his book From Rogue to Everyman: A Foundling's Journey to the Bastille, around two-thirds of children placed in Paris orphanages died in their first year. A significant number of the surviving third would not have made it to adulthood, given that deadly illness was a reality for most Parisians, and the very young were most vulnerable. I don't have statistics on this, but see David Garrioch, The Making of Revolutionary Paris (especially the second chapter) for more information on the various illnesses that plagued the city at this time.
This sounds pretty shocking to us, but it's worth remembering that infant mortality in Paris was somewhere in the range of 35 to 45 percent at this time (according to Daniel Roche, in The People of Paris). A foundling's chances of survival were worse than those of the average Parisian child, but, sadly, those chances were pretty abysmal to begin with.
Child abandonment may not have been a death sentence, but it did worsen a child's chance of survival. Most parents who abandoned their children really didn't have a choice - most of the time they simply couldn't feed them. Rousseau, while he may not have been wealthy, also wasn't destitute. He could have given his children a better chance at life, but he chose not to do so.
For more information I really recommend the David Garrioch book I cited above, as well as Arlette Farge, Fragile Lives: Violence, Power and Solidarity in Eighteenth-Century Paris. Sorry, I'm too tired for properly formatted citations right now.