An Underweight Child: What Parents Need to Know

What Being Underweight Means

A child is considered underweight when their body weight is lower than what is expected for their age, height and sex.

For children and adolescents, this is usually assessed using a Body Mass Index (BMI)-for-age chart, which looks at how a child’s weight compares with others of the same age and gender.

Here’s how to calculate your child’s BMI:
weight (kg)
――――――――――
height (m) x height (m)

• Children between the 3rd and 5th percentile are considered underweight
• Children below the 3rd percentile are considered severely underweight

Doctors and healthcare professionals use these charts because children grow at different rates. A single number on its own doesn’t tell the full story – patterns over time matter more.

Why It Helps to Address It Early

When a child is underweight, it can affect more than how they look. Some children may:

• Develop physically at a slower pace, with less muscle strength
• Fall sick more easily as their bodies may not be getting enough nutrients for strong immunity
• Have lower energy, which can make it harder to concentrate or keep up at school
• Miss out on key nutrients their growing body needs

Spotting this early gives parents time to support healthy growth through a well-balanced diet and healthy lifestyle habits.

Common Reasons a Child May Be Underweight

There isn’t a single cause for a child being underweight. Often, several factors are involved.

Body build and genetics

Some children naturally have a smaller frame or a higher metabolism. If parents are naturally slim, a child may also find it harder to gain weight despite eating regularly.

Not getting enough nutrients

Even when a child eats often, meals may lack essential nutrients needed to support growth.

Higher metabolism

Some children burn calories quickly, even at rest. If their calorie intake doesn’t keep up with what their body uses, weight gain can be difficult.

Poor appetite

This may be influenced by:

• Naturally smaller appetite
• Irregular mealtimes or frequent snacking
• Picky eating
• Stress or emotional factors
• Illness and recovery

Understanding the reason helps guide the right kind of support.

When to Check In with a Professional

It may be helpful to speak with a doctor or dietitian if:

• Your child remains underweight despite consistent efforts
• Their growth seems slow or has stalled over time
• You’re concerned that they may not be getting enough nutrition

A professional can look at growth patterns, rule out underlying issues, and suggest practical next steps.

Read on for practical steps to help your child gain weight safely and steadily.

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