I can only relate to squirrel behavior here in the western U.S., but, with that as a guide we find that all varieties generally have to "sets" of offspring each yera. Here, it's in April and then again in September. The young ones don't leave the nests until they are fully furred and can exist without their parents.
So... our April is likely much colder than your's and the young wouldn't appear outside until mid May or so. The nestlings that do come out tend to stay close to each other and we've seen 4 or 5 chasing one another up and down trees. We will see numerous squirrels together after late April or so and then again in October.
Since they don't hibernate, they often stay "indoors" until it warms up enough for all of them to venture out at once...