Should a child's height percentile always be higher than weight percentile?

No: There is also a weight for height graph that can tell if the child weighs more than he should for his height. But a child could be -for example-25% height and 50% weight and still fall within normal guidelines. Kids tend to change rapidly mad may get heavier just before a growth spurt, . If the doctor says your child is overweight please take it seriously. Work on exercise ; eating habits.