**Core Concept**
The World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) have established specific criteria for defining obesity in children based on their body mass index (BMI) percentiles. This is crucial for early identification and intervention to prevent long-term health consequences.

**Why the Correct Answer is Right**
The correct definition of obesity in a 2-year-old child is BMI >95th percentile. This is because BMI percentiles take into account the child's age and sex, allowing for a more accurate assessment of their weight status. For children under 2 years, BMI-for-age percentiles are used, whereas for older children and adolescents, BMI-for-age and sex percentiles are used. In this age group, a BMI >95th percentile indicates that the child's weight is higher than 95% of children of the same age and sex, suggesting obesity.

**Why Each Wrong Option is Incorrect**
**Option A:** Weight for height more than double of expected is not a valid criterion for defining obesity in children. This measure is more relevant for assessing dehydration or malnutrition.
**Option B:** Weight for age more than double of expected is also not a suitable criterion for defining obesity in children. This measure can be affected by factors such as stunting or wasting, making it less reliable for obesity diagnosis.
**Option C:** BMI >30 is not a correct definition of obesity in children. While a BMI of 30 or higher is considered obese in adults, this threshold is not applicable to children due to their varying growth patterns.

**Clinical Pearl / High-Yield Fact**
It's essential to note that BMI percentiles should be plotted on a growth chart to assess a child's weight status over time. This allows healthcare providers to identify trends and make informed decisions about obesity prevention and treatment.

**✓ Correct Answer: D. BMI >95th percentile**