Yes, He’s omniscient, but also originally planned for their children to be there.
Otherwise, he would never have given the command “be fruitful and multiply” before the fall.
God cannot be mocked, he was not giving them a decoration command. The command was in the Garden, he intended the Garden to be filled with children (as well as the rest of the earth).
Consequences = punishment, they’re the same thing in this case because God had imposed both
No, the Church teaches that God is pure act (actus purus) without any admixture of potentiality (actus purus sine omni permixtione potentiae). His acts are not contingent on mankind. The plan of salvation of fallen mankind was even before creation.
Adam and Eve were given a blessing not a precept.
Catechism
2331 "God is love and in himself he lives a mystery of personal loving communion. Creating the human race in his own image . . … God inscribed in the humanity of man and woman the vocation, and thus the capacity and responsibility, of love and communion."114
“God created man in his own image . . . male and female he created them”;115 He blessed them and said, “Be fruitful and multiply”;116 "When God created man, he made him in the likeness of God. Male and female he created them, and he blessed them and named them Man when they were created."117
Haydock Commentary, Genesis 1:28
Ver. 28. Increase and multiply. This is not a precept, as some protestant controvertists would have it, but a blessing, rendering them fruitful: for God had said the same words to the fishes and birds, (ver. 22.) who were incapable of receiving a precept. (Challoner)
— Blessed them, not only with fecundity as he had done to other creatures, but also with dominion over them, and much more with innocence and abundance of both natural and supernatural gifts.
— Increase. The Hebrews understand this literally as a precept binding every man at twenty years of age (Calmet); and some of the Reformers argued hence, that Priests, &c. were bound to marry: very prudently they have not determined how soon! But the Fathers in general agree that if this were a precept with respect to Adam, for the purpose of filling the earth, it is no longer so, that end being sufficiently accomplished. Does not St. Paul wish all men to be like himself, unmarried? (1 Corinthians vii. 1, 7, 8.) (Haydock)