A 3-year-old boy from rural Maharashtra is brought to the pediatric clinic by his mother for poor weight gain. He weighs 11 kg and is 85 cm tall. His birth weight was 2.8 kg and birth length was 48 cm. The child was exclusively breastfed until 6 months, then introduced to home-made rice and dal. On examination, he appears alert, with mild wasting visible on the arms and chest. His mid-upper arm circumference (MUAC) is 12.5 cm. The mother reports he has had 3–4 loose stools daily for the past 2 weeks. What is the most appropriate classification of this child's nutritional status using WHO criteria?