I read that somewhere. I kind of did a little "le gasp wtf" thing then realized that the internet isn't the best source of knowledge of anything. Haha.
I can't believe that about Rugrats. Angelica was so mean to them during the shows that I can remember, and the parents were always to keen to the kids. And it doesn't explain where Dill, Tommy's little brother comes into play and stuff. I want to find the spongebob theory now!
Okay, so I also watched The Rugrats Movie last night, to see if this theory seemed true at all. And it's really unclear if this theory could be true at all. But it's probably not, because the parents pay attention to the kids. And, if they were Angelica's hallucinations, then the parents wouldn't be able to see them. If that makes you feel a little better.
That is not a theory that any of the creators of The Rugrats have even hinted at may be true. That's just someone who has started a silly rumor, just like there are rumors about how everyone in Whinnie the Pooh are really drug addicts since they all act like separate people who are high (Piglet, LSD, worried all the time, etc). It's not true, period.
Also, it doesn't make sense because as far as I remember Tommy has a brother Dill, further down the line, so what's the theory for Angelica supposedly creating him?