I hate the word "kiddo." I'm not even sure why. In my mind, though, it should only be used somewhat sarcastically. "Tough luck, kiddo." It could also be used when expressing sympathy: "I'm sorry, kiddo. I know you're disappointed."
What will grates on my nerves, however, is using the word when not addressing a child. "What are the kiddos doing today?"
I cannot possibly explain why I find this so deeply unpleasant. But, there you are.
Acceptable alternatives include: kids. children. kidlets. young'uns. yotlots (youth of today, leaders of tomorrow). tiny creatures. etc.