So, I know you're not updating anymore but just cause i'm having problems, how do you pet the chao? Anytime I try to use my finger I just pick them up, and it's more frustrating to me to pet since i'm not sure WHAT i'm doing wrong.
I was able to pet them by pressing and holding the chao! Maybe it would work for you as well? :)
I tap them and it seems to pet, if I press and hold it tends to pick them up, i'll try through.