How do you now whether a chao is a boy or a girl because I have this one..

Actually, contrary to popular belief, chao have no gender to speak of. Remember this is an "everyone" rated game, and these creatures are Artificial Life (AL) character's. They also don't have any reproductive organs to speak of. On top of that, I will re-emphasize that this is an "everyone" rated game. Because of this boy/girl gender question, I will explain to you how the coloration work. The chao change their general colors based on what you give them, both animal-wise & chaos drive wise, and also on how they are raised by you like if you hit a chao a lot they will turn evil from the mistreatment (this happens whether or not you are Dark or Hero, attacking a chao is just plain evil, so this act of cruelty turns them dark inside...probably from choosing to repress these dark memories; heck, I might do the same if I was a chao, but then I would leave like most chao do). Just as well it also depends on which type character you use: Dark (Eggman, Rouge, Shadow) or Hero (Sonic, Tails, Knuckles), or a mixture of the two groups. As for your mating delemna, both of them have to be mature, i.e both of them have to have evolved at least once. And since you used the heart fruit on both of them, well, you just wasted a heart fruit... You only need to use one and then put a chao next to either one that has a flower circle. Just pick one of them up and put it next to the other. They will mate eventually and an egg will be formed. Good job, happy parenting!

This is Dr. Eggman saying that being bored is better than being dead....unless you are bored to death...but that's something else entirely. =P