We have a play date tonight with 2 couples and their kids. The kids are all younger than my oldest but she has fun playing with the one little girl. What age are you comfortable letting the kids play out of parental sight, but within 30 second distance (bedroom?)

Normally we let DD who is almost 4 play independently in her room, her friend is 2, so i'm not sure if she's old enough to play independent? Should I just set up an area with toys in the living room?