I believe that should be perfectly acceptable, and would be shocked if you were stopped. The offspring will not be entering unaccompanied providing you are a responsible adult over 18 years old. It would stand to reason within the rules that a child under 18 years old cannot bring a guest that is also a minor under 18. Our daughter currently has bronze and only 20TP's short of silver with 4 months left. If any of the free domestic child ticket offers that match the booking class of the adult come on I fully intend an N class rtn to gain her the required points for the simple reason our membership years overlap by 6 months, and may at some stage come in handy for guesting purposes......hopefully not but you just never know. She will also enjoy the trip to the T5 soft play area!