Changing font size of tabbaritem

I recommend a better way:

[yourTabBarItem setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:
    [UIColor whiteColor], UITextAttributeTextColor, 
    [NSValue valueWithUIOffset:UIOffsetMake(0,0)], UITextAttributeTextShadowOffset, 
    [UIFont fontWithName:@"Helvetica" size:18.0], UITextAttributeFont, nil]
    forState:UIControlStateNormal];