Most people are aware of these laws, but many people do not realize that cartoons, drawings, and animated depictions – including anime movies and manga comics or novels – of children engaged in sexual activity are also considered child pornography, and you could be charged with a crime for viewing such images.
Answering the question: Is anime safe for kids? Not all anime is sexualized. Anime is simply an art form. However, parents should know that there are many genres within anime that are sexualized and even pornographic. That's why it's so important to research each anime show your child wants to watch.
However, there is nothing to worry about if children watch anime in moderation. Not only with Anime but with any entertainment genre, spending a lot of time is detrimental for the mental health of anyone, not just children. You can set a time for your child to watch a movie like after homework or on the weekend, etc.
Originally Answered: Why do people think anime is childish? Because most people are used to animation in general being childish. Often times animation isn't respected as an art form, even though it was intended for everyone at the time of its conception with things like the early Looney Tunes and Disney cartoons.