Is it normal for a child to lose weight? At 9 months old she weighed 1…

Is it normal for a child to lose weight? At 9 months old she weighed 10 kg, at 10 - 9.5 kg, and now 8.7 kg. She eats small portions during breastfeeding. She's still very active, but can't lose this much weight because of that. Who knows why?