I don't know about "looking at", as it can be hard to see them in action at that time.
But if your son is draft eligible (whether in HS or college), it's not unusual for home visits to happen over the winter, especially if the player is in the running to be a very early pick. Many teams as well as the MLB Scouting Bureau do this as a "getting to know you" thing, maybe evaluating the player's home life, gauging whether the player is signable, and perhaps even collecting a specimen or conducting other tests.