Grizzly bears typically have their cubs in the winter, while the mother bear is in hibernation.
Specifically, the cubs are born in January or February while the mother is still in her den. The cubs are born small and helpless, and they rely on their mother's milk for several months before they are able to venture out of the den.
The mother bear will usually give birth to two or three cubs at a time, and she will care for them in the den until spring, when they emerge and begin to explore their surroundings.