A 6-month-old infant presents with a 2-day history of watery diarrhoea (6-8 loose stools per day) and 2 episodes of vomiting. He is breastfeeding well but seems slightly less active. On examination, his temperature is 37.8°C, capillary refill time is 2 seconds, and mucous membranes are moist. He has no signs of severe dehydration. According to NICE CG84, what is the most appropriate advice for the parents?