Here are my thoughts on this.
1. The Rugrats aren't "all-grown up". They're only around 13.
2. Here's what I'm thinkin-- Nickelodeon should quit making shows about teenager's lives. Because Nickelodeon is a kid's network, and they would have to keep the obsceneties down. So once they do that, the show about real-life teenagers becomes a show about a little kid's fantasy of a teenager's life.
Moral of the post: If you have to dumb a show down for the kiddies, you might as well not make a show at all.