Chihuahua puppies should be at least 8 weeks old before given up for adoption, although waiting until they are 10-12 weeks is better. Before allowing them to leave their mom, they should be able to eat hard puppy food on their own.
Puppies are not supposed to be removed from their mothers for at least 6 weeks after birth. They are to receive nutrition from the mother's milk. Normally puppies can begin to eat soft-canned food as as supplement to the mother's milk at around 4 weeks.
It is common for a dog to eat the placenta of the puppies after she gives birth. On rare occasions, a dog will eat her puppies when they die or right before death because she instinctively knows that there is something wrong.