I went to both parties in 2000. The Universal party is probably too scary for your kids. They recommend that no children under 13 be brought as it is REALLY SCARY. My two sisters (20 & 22) were terrified. The park is almost completely dark & there are guys with chainsaws in the shadows. Scary people & monsters hiding everywhere. It's really too much for a kid.
Disney on the other hand is really great for kids. They have tame thrills like the headless horseman who leads the parade. Nothing is going to come out of the dark and grab you here. I personally would not take children to Universal's party but would definitely go to Disney's.
Plan on going again this year. Will take the kids (11, 9, 9, & 1) to Disney. Then leave them with Granny so the rest of the adults can go to Universal.
Hope this helps.