Yes, children's programming is more liberal now than in the past due to progression of the times. Children today need to be more open-minded to function successfully in the world, and programming is addressing more modern issues like homosexuality and other issues to prepare for life in the real world.
Children's television shows aren't overly political, so I wouldn't say they are extremely liberal or conservative, but they are somewhat more liberal now. There is more diversity on children's television programming. Some people may say this is liberal, but it really is just reflecting the fact that diversity exists - it doesn't really take sides on major or adult issues.
Disney just recently introduced a character on a new program who has two moms. Even as early as the 1990's eras of cartoons were showing single-parent households as shown in Rocket Power. In the cartoon As Told By Ginger, which ran from the late 90s to mid-2000s, Ginger is shown to having a relationship with a boy from a different racial background. These concepts are much more liberal than the early Disney cartoons, or Saturday morning cartoons of years past.
I believe children's television programming has changed, but I think it is unfair to label it as liberal. I think you could say it is more violent, but it is hard to ascertain why this is happening. If anything it has more to do with corporations providing what sells and things don't sell unless the public supports them and buys the product. Parents aren't turning the TV off for these programs so it is assumed they like them and would want more.