This is really airport and airlines dependent.
I am UA gold and United Club member, my wife and two kids are not. Our international lounge access experience thus far...
1. Air Canada: member + 1, strict, no exception.
2. Star Alliance Lounge in LAX: member + 1, strict, no exception
3. EVA Air in TPE: member + 1, strict, no exception
4. Contract lounge in Venice: member + 1, and kids < 12 welcomed free of charge
5. Air China Lounge in PVG: member + 1, and kids < 12 welcomed free of charge
You really have to just ask!