Usually the young blue jays will leave their nest when they are about 17 to 21 days old. The parents will keep feeding their young ones for about a month or two.
Blue jays will communicate with each other using their voice and their body language. When their crest is down low everything is OK. But if they are not happy they will raise their crest up high.
The parent is flying off to find young one more food.
The photos here was taken in August.