No one's going to change my mind that Universal has enough geared towards kids. I'm not a parent yet, so maybe I don't know what I'm talking about,
I think you hit the nail on the head when you said you were not a parent. Consequently, you can't relate to today's children and what they might enjoy.
I despise Shrek (and will hopefully pass that hatred on to my kids

). Hanna Barbera's simulator was infinitely better than the Jimmy Neutron one they have now.
You feel the Hanna Barbera ride was better than today's Jimmy Neutron. But I would bet that would be because the Hanna Barbera ride featured cartoons that you were familiar with (Flintstones, Jetsons, etc). I would also guess that as an adult, you don't spend a whole lot of time watching Nick. So the characters in the Jimmy Neutron ride would not be as familiar and beloved to you as they are to today's kids. My kids love riding through the Rug Rats house with Jimmy chasing the evil Ooblar, visiting Fairly Oddparents, Hey Arnold and Spongebob.
You hate Shrek, however, many kids LOVE Shrek. This is a wonderful ride for all ages.
You can't beat the Suessland and all the interactive play areas for the little ones.
My kids have been doing WDW and Universal at least 2x per year for years now. My youngest started Universal @ 2. Obviously, he found plenty to do there as a toddler or we wouldn't have kept going. The kids love both parks, however they much prefer Universal.
From my standpoint, what sets Universal apart from Disney (and not in a good way, in my opinion) is the lack of "family" feeling I get from there.
Our family would strongly disagree with you here. We find the Universal parks just as family friendly and "magical" as WDW. Yes, they are different from each other, but both have a wonderful quality to their theming. They are not the same parks, so they shouldn't be clones of each other. They are different, should be appreciated for their own special qualities, but both are wonderfully themed with great attractions for all ages.
Don't get me wrong, their ET ride is one of my favorite theme park attractions anywhere and it would certainly appeal to a younger crowd, but I still think that young ones would be better occupied at Sea World.
Again, I would have to disagree with you here. My kids did love Sea World when they were young. However, when they were old enough to really understand the science behind it is when they really started enjoying it. My older kids love to do the special tours such as the Predator tour.
I say the above as a person that enjoys Universal (I'm not a Universal basher), but I also say so believing that Universal is not a park I would take my kids to until they were at least 10-12.
That would be such a shame as there is SO much for young children to do. I hardly think that a 10 year old would enjoy dancing with Barney, but perhaps your future children will actually prefer that over Shrek
However, honestly, I would skip both and just spend more time at Disney. Lord knows that there's plenty for the 14 and 18 year old to do there, too.
I think that also depends on the teenager. My 16 year old would argue very strongly with you over that. He gets bored very easily at WDW. When we were there in November for a family reunion, the majority of the over 10 set much preferred Universal over Disney.
OP, since you have both young children and teens, I think Universal would be a better option for you, as it has more things to entertain both the young set and the teens. If it were just the two little ones, I would say it would be a toss-up, but since you have the older ones, I think Universal is a much better bet. And to answer your original question, Universal has plenty to do to keep a toddler entertained for a day.