In my children story the squirrel addresses his friends (a boy and a girl) as 'guys'? Is it okay to use that word?
The public broadcasting cartoon Wild Kratts (aimed at young children) refer to a mixed sexed group as guys in almost every episode. I've not seen its usage in young children's books (I have young children). Then of course, if you're talking Wimpy Kid then it's in there and its usage is acceptable. I would rather see a different term or phrase used if it's a young children's book, but that's a biased opinion. I think it's fine in tween/teen dialogue in particular.
The kid's show "The Electric Company" from the 70's PBS channel started every episode with the catch phrase "HEY YOU GUUUUYYYYYS!", and I turned out fine. At least in the US, the term 'guys' is understood to refer to a familiar group of any sex, any age. Well, maybe not very respectful for the elderly.
I'm going to go with YES! In America and England (I have numerous English friends, but in real life and over the internet to reference this from) the word is used to encompass all sexes. I've seen girls refer to a group of only girls as "guys," I've seen boys refer to a group of only boys as "guys," and I've seen them mixed. Now that I've started college, I've also found that my professors tend to refer to our classes as "guys," despite the fact that they're all relatively evenly mixed. Usually, I think, this will be referring to a younger group of people, though. A 60-year-old man will most likely not refer to his peers as "guys."
I can confirm that this has been common usage amongst young people in the UK for at least 30 years, so some of them are no longer all that young. I can place where and when I first heard it to London in 1981.
