Son plays rough

My son is my only child (#2 coming this fall) and with COVID restrictions this past year, he’s been home with me and his dad everyday and maybe played with other kids (older cousins) 3 times total.

Yesterday, we had a family Easter egg hunt now that most family members are vaccinated and he loved seeing the kids, was so curious and wanted to join them but he has a major sharing problem.

Anytime a child took a toy he wanted or played with a toy he brought from home that was his, he would go up to them and hit them or throw a toy at them. Me and his dad would obviously intervene so no kid got whacked off the head with a toy truck, but I feel so guilty because he’s been home with me.

Once the weather warms up I am going to arrange some play dates but until then how can I work on his sharing skills? He plays so nice with me and when my mom comes over to visit I just think it’s a kid thing.