You can wean puppies at 8 weeks of age.
3 months that is 12 weeks is better
The bitch (aka mother) will let you know when she is ready for the puppies to be weened. She will growl at them when they try to nurse and run to avoid them. It is safe to ween at 6 weeks as long as the puppies are eating puppy food and drinking water well so that they do not get under nourished. When you ween them also make sure that you soak their puppy food at least once a day and mix a little spoonful of canned food in there so that they get the fats that are needed.