5yo weighed 40.5 in june 42inches she now weighs 39.5 and is 42 3/4 inches. she did have vomiting and diarrhea this past week. dr not concerned. ?

Can Occur When Sick: Acute illnesses such as diarrhea and vomiting can cause mild weight loss which usually recovers after the illness passes. Most likely the doctor was not concerned if she has otherwise had good weight gain prior to the illness and did not appear prominently dehydrated. Most important thing is adequate fluids and to return to your doctor if her illness worsens or she not does regain her weight.

Not important: The parameters that do not fluctuate up AND down in kids are head size and length.I see the kid grew almost an inch, which is a good sign.Being down 1 lb in a 40 pound kid could be the effect of the illness.The fact that she is on the lower end of the weight range for age likely bothers you more, but this is not unusual with what you have reported.