Aah I feel you lah, same worry I had with my second one, 6.5kg at 10 months is on the lighter side even if dia makan well, so I'd say best to check with the paediatrician first to make sure everything's okay absorption-wise, sometimes ada hidden issues macam food sensitivities. A few of us tried adding more calorie-dense foods like avocado, egg yolk, and full-fat yogurt into their meals, plus frequent feeds if you're still breastfeeding, but honestly the doctor should rule out anything else before you go heavy on the feeding side.