Tetsuwan Atom (1980)

Both anime are about a boy who's a hero and saves the day in a futuristic world. They are also both retro anime. The difference between Astro Boy and Chargeman Ken are: - Astro Boy is a robot with emotions and Chargeman Ken is just some kid with powers that comes out of nowhere - Astro Boy shows mercy on his enemies while Chargeman Ken doesn't - Astro Boy is clearly a better anime than Chargeman Ken 

Also created by Osamu Tezuka, this anime has the same emotional impact and resonance, as well as a similar protagonist. 

Little cute flying kids who save the world with their superpowers. Both Astroboy and the Powerpuff Girls are child-looking, well-behaved, and were created in a laboratory by a scientist who is like a dad to them. Even though PPG is more light-hearted and may seem a shoujo, both series can be targeted as shounen.