Baby weight stagnant

Hi my baby is coming to 8 months but his weight has been tanking between 6.7-7.1 fluctuating throughout the last 2 months. Personally I feel that like me, my baby is just on a smaller side and as Long as there’s no drastic drop in weight it’s fine. My wife is very concern as she sees other babies in her mummy chat group grow bigger and faster. Should we be worried?