Pokemon.
Similar to all the children's books to movies being done lately, like Harry Potter, or Bridge to Terabithia, or the Spiderwick Chronicles. Three young kids go on a world-wide adventure and battle amazing creatures.
Based on Pokemon Red/Blue, and only featuring the first 151 monsters from that generation of games. Then the sequel can have the Gold/Silver monsters, and so on and so forth. Handful will be mainly featured like Pikachu, Charizard, and Geodude, while all the rest will serve as easter eggs or cameos throughout the movie.
The premise: 500-1000 years in the future after a devastating disease managed to wipe out every species of animal in the entire world. Humans were immune to it, and before all animals went extinct, scientists gathered a genetic "Noah's Arc" of DNA samples from all animals, as we need them for our ecosystem, food, and companionship. Legend has it that an extraterrestrial life form was used to help clone animals. (Mew) After cloning animals it was found that their genetic structure could be broken down and stored in containment units. And if you placed your genetic code on the units, they would obey your commands. After everything settled, "Pocket Monsters" used for battling became the number one sport on Earth, and a way of life for many. After centuries, "Pokemon" began to evolve in increasing rates, until eventually, even in their own lifetimes. They repopulated nature and continue to evolve and develop new species. There's a lot of fields dedicated to Pokemon, like scientists, doctors, breeders, and of course trainers. And the world is so peaceful in the future that you could leave your home at age ten, after completing the equivalent of a bachelor's degree from the future's very advanced education system, and it would be normal to ride your bike around the world.
The movie starts out with Ash Ketchum (unknown or someone like the kid from Terabithia) leaving starting his journey from Pallet town with his new Pikachu that was given to him by his neighbor, Professor Oak. Oak promised him a charmander, but his grandson Gary demanded it. So on the way back to the lab Oak and Ash encounter a Pikachu in the wild that can't be captured or contained in a Pokeball. Pikachu is the first-ever documented naturally-born Pokemon. Pikachu makes friends with Ash anyway, and still listens to him, and Oak entrusts Pikachu to Ash's care. He goes to Pewter City and meets Brock, and then later Misty at her town. There'd be a montage of gyms, all straight from the game, with their trainers looking exactly like Lt. Surge, Sabrina, etc. Ash fights off Jesse and James, top agents from Team Rocket who were sent to capture the first ever naturally-born pokemon, which would change the world. They have Meowth, a pokemon genetically-engineered to speak English. It's hinted at that Giovanni, the leader of Team Rocket, is actually Ash's father (played by Robert Deniro.) In the end, Ash is competing at the Indigo League when Team Rocket attack and Ash fights Giovanni and wins, but loses the tournament to Gary. Setting up for the sequel where he'll train with his friends in a different part of the world.
I would give my freaking LEFT ARM to make this movie.