Robinson Helicopter; Undifferentiated or Other Model
Flight Crew Private; Flight Crew Rotorcraft
Flight Crew Last 90 Days 65; Flight Crew Total 5139; Flight Crew Type 76
Confusion
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
General None Reported / Taken
Human Factors
My wife and I planned a round trip to visit some friends at a church in ZZZ and have lunch after the meeting. Our granddaughter stayed the night with us prior to our flight the next morning. She travels with us often and enjoys the trips; and has flown with us since she was born. The next morning;  we arrived at the airport and boarded the aircraft along with our friend and his wife. I did a weight and balance; and it came out more than 200 lbs under the gross weight limit. I verified and center of gravity and weight were well within limits. My wife had our granddaughter sit next to her in the seat; and I made sure they were buckled. Together they weighed less than 170 lbs and seemed to fit comfortably in the one seat. We departed mid morning. We had a good meeting and lunch in ZZZ; and after lunch we all got back in the aircraft and buckled up ready to go back. It occurred to me that our granddaughter is now 6 years old; and even though she is approximately the same height and weight as when she was 4 and 5; she should have her own seat and seat belt. In the future I will make sure each occupant of age has his or her own seat and seat belt; so they can be properly buckled and restrained.
Robinson pilot reported improper seating assignment for a flight.