I can't see a way to change the font size of the labels on TabView bar items. I managed to achieve this on Android with:

    tabView._tabLayout.getTextViewForItemAt(0).setTextSize(10);
    tabView._tabLayout.getTextViewForItemAt(1).setTextSize(10);
    tabView._tabLayout.getTextViewForItemAt(2).setTextSize(10);

but the same approach on iOS (using the appearance proxy: UITabBarItem.appearance().setTitleAttr...) didn't work, I can't be sure what's going on under the hood (are our changes being applied and then overwritten, or just not working outright), but the approaches on Stack Overflow articles that appear to work for regular iOS projects don't seem to be working here, which is strange.