1.) Because Clone Wars was all the time super mature? They already killed a handful of Troopers in these first scenes. Sorry that there was no blood or body parts lying around or that no one is reminiscent of his horrible and brutal back story in which his whole family was murdered. I like gritty and dark movies just like the next guy, but it should be in the right context. And if you don't like the kid or the witty one-liners (or the colorful characters in form of Zeb and Sabine), I certainly do not know why you watch Star Wars anyway?
2.) It's a cartoon show for a broad audience, primarily for children/teenager. Both Clone Wars and SW Rebels were never aimed at an older target group. Star Wars generally has a lot to do with merchandising because kids rather tend to buy toys than some men-children. The producers still acknowledge that also older people watch the show. I don't think that you watch the new CGI Teenage Mutant Ninja Turtle show, but they recently had an episode which referred to "Big Trouble in Little China". This is the perfect example of a small nod to the older audience.
If you have not seen the first episodes, why bother anyway to post your shallow opinion except to show how mature you are? You're post is missing a "It's all Disney's fault" sentence I won't really discuss this further on because I simply think it's a matter of openness to something new. Just count it as a general statement to all of these "Star Wars before was sooo mature but now its for babies".
Nah, I think they just want him to be more exotic with his blue eyes/hair instead of the typical whitey-white Star Wars human. Besides Lando and Mace Windu, the majority of people look quite the same (Obi Wan, Anakin, Padme, Han, etc.) and because Rebels' crew is focusing on a diverse aspect, it makes sense in my opinion. Plus I don't know why someone would have an issue if he looks like Aladdin?