I agree with Max. Because most families are REALLY busy, there just isn't as much playing at each other's houses anymore. I will say my boys have a bunch of friends that they hang out at the park with if they don't have practice, but even then it's not every day and they go to different schools. I think it's just a sign of our times.
It's ok. my mom never let me or my sisters go to anyone's house and my sisters were very popular. They had and still have plenty of friends. I'm just not a social butterfly but even still people remember me from school that I never even tasked to.
At 3rd grade, I think your child is old enough to learn how to start reaching out to kids outside of school. With my son, I encouraged him to exchange phone numbers with classmates and start calling them to arrange get togethers outside of school. It's an important skill to have, and I don't think my parents taught it to me.
When we were kids all we had was to play outside and other's homes..
i wouldn't worry unless he starts to get reclusive. My DS (10) has 3 boys in this neighborhood that he likes to play with... It is very similar to how when I was a kid, because I don't allow my kids to just sit around the house. My DD is 15, she doesn't really "hang out" with anyone except her BF which doesn't live in this neighborhood..but she has all kinds of friends at school, and all chatty on the phone and text...