When your chao is in the egg, how you treat the egg affects its face and personality. Here is the different personalities and faces:
Don't touch the eggs, just let them hatch with time.
The normal chao face is kind of tricky, but I got used to it and it's normal for me now. You have to shake the egg for about 4-7 seconds, but no less or more.
Evil Eyes Face
Jump around the garden with the egg (Perferably with Shadow), then set it down.
Sleepy Eyes Face
Shake the egg for about 2-5 minutes.
Upside Grin, Evil Eyes Face
Follow the same steps as the Evil Eyes Face, but do it for 2-5 minutes.