Or HaChaim on Exodus 10:8/אור החיים על שמות י׳:ח׳

1 לכו עבדו…מי ומי ההולכים "Go and serve…who are the ones going?" Pharaoh asked a rhetorical question; it had not occurred to him that they would demand that all of them should go. This is why he had simply said: "go and serve" without limiting the ages or sexes of who was included in that offer. He had naturally assumed that only adult males would particpate in the ceremony under discussion. This is why he said later: "your menfolk may go because that is all you ever requested." He did not even want all the adult males to go.