The author says that a talmid chochom related to him that the Chazon Ish was only matir powdered milk for children, at a time that milk was scarce, at the beginning of Israel’s statehood.
Goes back into L’chatchila vs. B’dieved. If B’dieved it is Mutar, then that is what it is (for those who are willing to go B’dieved). I don’t think (though I may be wrong) the Chazon Ish would have said children can drink camel’s milk.