What did the midwives mean when they told Pharaoh that the Ivriyods were Chayos?
Rashi #1 and Targum Yonasan: They simply meant that the Jewish women were agile, and by the time they arrived the babies were already born. 1
Rashi #2: They meant that the B'nei Yisrael were compared to Chayos, 2 who do not need midwives.
Seforno: They are themselves experts in midwifery, in which case they will know the moment we do something untoward, and will never call us again.
How did that justify sustaining the babies?
(EC): Pharaoh's instructions were that they were to kill the babies before they were born, 1 once they actually were born, there was no point in not sustaining them.
רש"י: משולות לחיות השדה: למה הוציאו הפסוק מפשוטו?
גור אריה: קשה מה בכך שהן בקיאות, וכי מילדת לא זקוקה למילדת?!
רש"י: משולות לחיות השדה: מה פרוש הדבר?