This verse is another of the Zichronos – the remembrance verses recited on Rosh Hashana. Most commentators see this verse as a criticism of the nation of Ten Tribes, referred to collectively as Ephraim. “Is Ephraim a favorite child? No!” The Daas Mikra (and others), however, interpret it as a form of praise. According to that interpretation, G-d is saying, “Didn’t you know that Ephraim is My favorite child…?”