The two children of Isaiah are two prophecies. And those prophecies are the topics of two sections in Isaiah 9:8 - 10:34. The first is the second named son, Maher-Shalal-Hash-Baz. His name means "Speed the spoil, hasten the booty" and is applied to the swift and soon coming fall of Syria and Damascus to Assyria. Isaiah 9:8 - 10:4 describe this coming event. The second section, 10:20-27, follows the prophecy of the first child, Shear-Jashub, whose name promises a remnant that will return.
The children's names are prophecies. These boys come forth announcing the coming judgment of God. Little children bring forth news and a new age. And to the faithful, another Child, Immanuel, brought forth another judgment upon unbelieving Israel, and with that judgment, the saving work of the Lord.