To get a Chaos Chao you have to get a chao that has gotten reborn twice. Give it one of every animal BEFORE you make it evolve. After that give it a Hero fruit for an Angel Chaos Chao, a Dark fruit for a Demon Chaos Chao, and a Chao fruit for a Chaos Zero like Chaos Chao (works best with a saphire egg). After that give it normal fruits until it evolves (lvl. 7-15). The animals are as follows:
Blue Group-All Around
Racoon
Skunk
Ram
Green Group-Run
Bunny
Hedgehog
Cheetah
Red Group-Power
Tiger
Bear
Gorilla
Purple Group-Fly
Condor
Parrot
Peacock
Black Group-Ghost
Half-Fish
Skeleton Dog
Bat
Orange Group-Legendary
Dragon
Unicorn
Phoenix
This works with any kind of egg but the chao MUST like you.