Can you name some examples?
Based on what I've been seeing, American kidvid producers seem to be steering away from female leads, not towards them. The Mighty B! is the only recent example of an American animated series starring a girl, and that show didn't perform well.
The Big Three animation channels (Cartoon Network, Disney and Nick) are clearly favoring boy-centric shows right now. In fact, a recently auditioned cartoon for Nick, The Modifyers, was allegedly rejected because it's protagonist was female. Similarly, Craig McCracken claims that one reason why his wife Lauren Faust's project Milky Way and the Galaxy Girls has yet to receive a TV show is because currently the kids' networks aren't interested in shows tailored for girls.
Sure, many of today's cartoons feature female characters, but many of them have minor supporting roles or they're just one face in the crowd, secondary appendages to boy characters. Chowder and Flapjack, for example, each have some female regulars, but the main characters, the ones who get the lion's share of the laughs and stories, are male. The upcoming Adventure Time likewise features a girl or 2 in the cast, but its' headlining stars are both guys.
Things are indeed better for female characters now than they were in the 40's or the 60's or the 70's, but I wouldn't say that the gender barriers have been broken yet. When we start getting some Phineas and Ferb or Chowder or Flapjack or Ben 10 or Generator Rex type shows starring girls, in which the leads are females and not just the sisters or the mother figures or the crushes or the sidekicks who dole out friendship speeches, then I'll say the playing field has become level.