The last time I went to Universal Studios in the fall there weren't too many families. I'm not saying that you won't see *any* kids at Universal during the fall, but since school is in session the crowds are noticeably thinner. (And before anyone gets upset, I don't have any kids, but I do love them.....I'm just saying that the family crowd is replaced by more young couples around this time.)
One father I talked to while waiting for a ride said he pulled his son from school every year around that time just so they could go to Universal and get more out of the park, then if they went during the summer peak time and you had to wait hours for most rides.
The nice thing about going to the theme park in the fall, besides the shorter lines, is the weather in FL starts to get cooler during the day -- still warm that you'll be wearing shorts -- but not as humid. Then again, it can get out right chilly in central Florida around this time, so be prepared with long pants and a sweater as well, especially for early morning and into the evening.
If you are a FL resident they usually have special offers on discount admission and multi-day passes.
They also host the Halloween Horror Nights until the end of October. This year they're "Sweet 16." I've never been because I'm a scaredy cat -- doubt I'll ever go.