I have not stayed at the Nick Hotel, but here's some info about the other stuff.
Wet N Wild is so much fun. If the 8 yr old can swim, it will be more fun.
Lots of the rides there have height restrictions, but there is an area just for toddlers and little kids. Visit their web site at wetnwildorlando.com
Universal is awesome. We always do WDW first and then Universal. It is more compact than Disney so you don't walk for e v e r to get somewhere.
They have some areas geared just for little kids Suess Landing and Kidzone.
Now, of course there are rides for everyone, more thrills, more shows, etc.
The new Simpson's ride is terrific.
There are water rides where you will probably get wet, so dress accordingly and bring a towel.
Have a great time on your trip. We always do!