You can ask them nicely. They will probably allow you with a “one time exception”. I saw similar DPs for travelers with children. So I don’t think you will get any rule written anywhere, but you will have to go and askI have 2 vistara gold infinite cards- me and wife, on boths' name.
But, will 11 yr old kid get access to the krisflyer lounge?
if kid will not get access, then there is no point!