If you're looking for anime similar to Wonder 3, you might like these titles.
Sorao is an ordinary student who lives an ordinary everyday life of a typical kid, accidentally makes friends with two aliens stranded here on Earth. His life changes as he decides to help them find a way to get home.
Bandar is a 17-year-old boy from Earth who lives on a distant planet, which is populated by human shape-shifters who feed off of vegetables and animal tails. Then violence breaks out, as invaders launch an attack on Bandar's new planet.
An alien from another world lands on Earth and befriends a human boy. Pipi tends to help his human friends by giving them sound advice and sometimes using his advanced technology when needed. This is a drama which is mostly live actors and scenery. The main character, Pipi, and many of the special effects are animated.
Four billion years ago in the Andromeda Nebula, an ambitious project was launched. The project was known as the Omega Program. The human race was the result of this project. But not only was the human race created but an evil force as well, and now the humans last hope the Delta Boy - the living avatar of the supercomputer that began life on earth - must save Earth. His only problem is staying alive long enough to save his future and that of all humanity.
The Nohara family is abducted by aliens from an advanced civilization who claim that Himawari is a legendary princess who will save the solar system. Unaware of the consequences, Shinnosuke signs a contract that allows her to be raised in the alien world. This forces him and his parents to go on a desperate quest to bring her back.
Dr. Tatsunoko leads an underwater exploring team for research on the mysterious radiation that's found within a giant clam. The research team opened up the clam and found a giant pearl that's the source of the radiation. Upon returning the pearl to the Tatsunoko Research Center, Dr. Tatsunoko & his daughter Asari found an object that resembles a medallion. It had a message in it stating that a being from the planet Parlum is inside the pearl they uncovered. Suddenly the pearl started to crack like an egg, and thus appeared before them was an unusual looking boy. In the medallion's message it mentioned that the boy's name is Ace, and with his flying silver ring used as an aircraft and a weapon, he is able to go on missions in order to protect Earth from threatening alien invaders.