Midrash for Exodus 1:12

...and when the Israelite women conceived, they would return to their homes. When they were about to go into labor, the women would go out into the fields and give birth in the apple orchards, as it is written: "I woke you under the apple [tree]" (Song of Songs 8:5). And the Lord Blessed be He would send an angel from the heavens who cleaned them and made them beautiful, just as a new mother grooms her infant, as it is written: "And as for your birth, on the day you were born..." (Ezekiel 16:4), and He grants them two round cakes, one of oil and the other of honey, as it is written: "And He [God] suckled Him [ The Children of Israel] with honey from the rock..." (Deuteronomy 32:13). And as soon as the Egyptians would become aware of this, they sought to kill them. And a miracle happened, and the cihldren were swallowed up by the earth, and bulls would come and plow the ground above them, as it is written: "Upon my back the plowers plowed" (Psalms 129:3). And once the Egyptians would pass, the infants would rise up from the mud like grass from the field, as it is written: "I have made you grow like the plantlings in the field..." (Ezekiel 16:7) And when the babes grew, they would flock to their homes in great droves, as it says: "And you came in all your finest and dressiest," (Ezekiel 16:7) - do not read "finest and dressiest" but rather "flocked in droves." And when the Lord Blessed be He revealed Himself at the Sea of Reeds, they were the first to recognize Him instantly, as it says: "THIS is my God, and I will praise Him." (Exodus 15:2).

And Pharaoh charged all his people, saying: “Every son that is born ye shall cast into the river” (Exod. 1:22). Thereupon, the Holy Spirit exclaimed: Who is he that saith, and it cometh to pass, when the Lord commandeth it not? (Lam. 3:37). Pharaoh decreed that the firstborn children should be cast into the river, but the Holy One, blessed be He, did not ordain that. On the contrary, The more they afflicted them, the more they multiplied, and the more they spread abroad (Exod. 1:12).

It is also written concerning them: And the land was filled with them (Exod. 1:7). That is to say, that even while they were suffering hardship, they increased and multiplied, by means of the mirrors in which they preened themselves before their husbands. They aroused their sexual desires despite the arduous labors they performed. They reared all the hosts that were to depart, as it is said: All the hosts of the Lord went out from the land of Egypt (ibid. 12:41), and also: The Lord did bring the children of Israel out of the land of Egypt by their hosts (ibid.,v. 51).