You're reading too much into this. 'Little' describes the girls.

# 2 This is the only logical meaning. The girls were young, probably in the 3 - 8 age range - that's what we call 'little girls'. The cats were just cats. Cats don't vary much in size. #1 Your first interpretation is unlikely. People and cats are on a completely different scale - so if we did want to specify that the cats were unusually small ones, we would say something like 'little girls and tiny cats" or 'small girls and little cats'. Your second interpretation is impossible grammatically. For countable nouns, 'little' can never refer to number. If you are referring to number, you would have to say 'A few girls and cats'. This would mean that there were maybe four or five girls and some cats. But this wouldn't mean 'only boys' and it wouldn't certainly mean 'nobody'. How can 'a few girls' mean 'nobody'? It's a very simple phrase and it means just what it says - some small girls and some cats. That's all. You are overthinking this!

Kenji, I *like* this post! You have a good instinct for noticing potential ambiguity, and I like your logical analysis. ^_^ Your instincts (I believe) will help you with English in general. Spotting ambiguity when you see it, and avoiding it in your own communication, is an important and far-from-common ability. Su.Ki has explained why *this particular sentence* is not ambiguous, despite perhaps looking that way on first glance. To pick up on your train of thought: "few girls and cats" means "not many girls and cats". "Few <something>" does not so much draw attention to the *number of items* present, but rather to *the fact that there are not more* items present. It is, in a sense, a negative way of looking at the number (like saying "the glass is three-quarters empty"). "Few people turned up to the gym today" "Fewer and fewer people are getting adequate exercise these days. That's not the same as "A few girls and cats." "A few" draws attention to the fact that there are some items present, while at the same time making it clear that the number of items present is not a large number. It's a positive, but realistic perspective, like "the glass is a quarter full". :) So you could say "Few girls and cats were playing in the park today" (I've added "today" so that "few" has the context that we're contrasting today's poor turnout to the usual case, where there are a good number of girls and cats playing in the park.). If the word "few" could be replaced with "little" (which it can't) then you'd have a nice ambiguous sentence there. But "few" means "small in number" and "little" means "small in size". For what it's worth, I would advise you to continue thinking as deeply as you are doing and/or as much as you like. The world is not in trouble due to overthinking. Quite the contrary. :) I actually don't believe it's possible to overthink; I've never seen anyone do it. The concept is an imaginary one, like the square root of minus one, or unicorns, but not as useful.