In Sonic Adventure 2 and Battle there are a certain number of Animal Chao in every level. I heard that collecting them all gives you an extra life, it didn't work, in one level Omachao says "collect all the animals and bring them to Chao Garden and all Chao will be happy"- that didn't produce any response in the Chao as far as I could see. Also, in one level there are 15 animals in the stage, how do you get 15 animals when you can only collect a maximum of 10 animals/Chao Drievs in any one level?
Getting all the animals in a stage doesn't give an extra life, and you never need to get all of them at once, anyway. Omochao's comment shouldn't be taken so literally; he just means that you should bring animals to the Chao Garden because they're used to make chao stronger and change their appearences.
~ Crazy C Lea