Комментарий к Вайикра 26:29

ואכלתם בשר בניכם, "and you will eat the flesh of your own sons." The reason the Torah repeats this statement by also writing: "you will eat the flesh of your daughters" is to tell you that even after having eaten the flesh of their sons their pity will not have been stirred and they will continue by eating the flesh of their daughters.

ואכלתם בשר בניכם, “you will eat the flesh of your children.” This curse corresponds to the blessing in verse 9 והפרתי אתכם, “I will make you fruitful.”Some commentators understand this as referring to children who are from highly respected families getting married to families of far lower social standing, by trading their superior ancestry for making an alliance with a wealthier family through marriage. If so, this would be the first curse.

It is also possible that the Torah stresses that the sons will be eaten first so that they would not try and escape when they observed their parents getting ready to eat their daughters. The daughters were weaker and therefore less likely to escape.

It is also possible that the reason the parents would eat the sons first is because according to Rashi on Shabbat 66 fathers display extraordinary leniency and mercy towards sons. Once they had consumed the sons they would certainly not feel any compunction about also consuming their daughters.