You know a few Aes Sedai will have kids despite the "discouraged behavior" ... hell, even an accidental pregnancy isn't out of the question, although I wouldn't be shocked if abortion was considered in these cases. Aes Sedai probably on some level realize that genetics play a role (there have been a few siblings in the Tower), so I imagine the fear of a male child would be rather high.
IIRC, the Companion tells us Basil Gill and his family were related to the Aes Sedai Jennet Cobb, she was revealed to be Basil's Great-Great-Aunt, descended from one of her brothers ... she was one of the Ferrets sent by Sheriam.
Obviously not a direct example, but it seems likely that there are some families of Aes Sedai floating around. IIRC Hawkwing's second wife was rumored to be a rogue Aes Sedai, and given that Siuan and Moiraine have to be told by their Ajah that the Blue specifically does not allow marriage for members, it also seems highly likely that other Ajahs (certainly the Green) allow for marriage, which you have to figure at some point will lead to a child or two.
Even with the issues of power level and gender. It's still a thing that is going to happen, but for all that... Wanting to keep pregnant sisters out of the eyes of the Tower's servants seems like a very Aes Sedai thing to do.
... Though all that would really answer is why said Aes Sedai brats aren't listed as coming from Tar Valon. Not why there aren't any Aes Sedai brats.