The Gemmorah (Yevomos 62b) brings a statement by R'Yehoshua:
...דתניא: רבי יהושע אומר נשא אדם אשה בילדותו ישא אשה בזקנותו היו לו בנים בילדותו יהיו לו בנים בזקנותו שנא' (קהלת יא, ו): "בבקר זרע את זרעך ולערב אל תנח ידך", כי אינך יודע אי זה יכשר הזה או זה ואם שניהם כאחד טובים
...Rabbi Yehoshua says: ... If he had children in his youth, he should have more children in his old age, as it is stated: “In the morning sow your seed, and in the evening do not withhold your hand; for you do not know which shall prosper, whether this or that, or whether they both alike shall be good” (Ecclesiastes 11:6). This verse indicates that a man should continue having children even after he has fulfilled the Mitzvah to be fruitful and multiply.
Do we have sources that discuss how many kids did the Rabbis (in the times of the Mishna and Gemmorah) had on average and their reasons for that?
This question is not about specific Rabbis, as we know about R' Akivah, R' Meir or R' Papa, but general trends and statistics.