Have a good touring plan for each day, get to the parks before the gate opening ceremony, explore the parks with cheerful eagerness, and you should be fine.
Last time we went to Orlando (2007) we went in late April/early May and pretty much had the Universal Parks to ourselves. The Disney parks are always pretty crowded, but the waits for the best attractions were not that bad.
Good luck!
I think you will be fine. Crowd levels will be as they are at the tail end of summer or better, so it should not be too bad at all. Remember, have a plan and arrive early...those are the keys to a successful day of touring. Oh, and remember to take a midday break when the park crowds are at their peak. A restful afternoon of swimming and napping is a great way to keep the family sane during an Orlando vacation!
Another thing, especially for the Universal Parks, is that you can purchase a Universal Express Plus pass for the day which is like having one fastpass at every major attraction in the park (Universal no longer utilizes a free fastpass system like Disney - you either buy a Universal Express Plus Pass, or stay at one of the Universal Resorts to obtain a fastpass). Proper use of the fastpass systems is always critical to a good tour when the parks get crowded.
If you are looking for some good books to help guide you on your journey, the two I like best are:
1) The Unofficial Guide to Walt Disney World 2008 by Bob Sehlinger & Len Testa (covers everything Disney in Orlando, and has a section on Universal and Sea World);
2) Universal Orlando 2008: The Ultimate Guide to the Ultimate Theme Park Adventure by Kelly Monaghan which specifically covers the Universal Parks and Citywalk.
Both should be readily available at the typical online book superstores.
Honestly, I have been to Orlando during several of the busiest times of the year, and if you have enough info, a good plan, and a sense of joyful determination, you can have a good time no matter when you travel!
Have Fun!
