If a sacral dimple is closed and is just a skin dimple, does this mean the child has a neural tube defect underneath?

No!: Minor shallow sacral dimples have no complications. They are a normal variation. Deeper pits or sinuses can become infected, usually when a child is much older. Further testing is only needed when dimples are large, deep and are unusual in location or appearance. Sacral dimples are found in 3% of normal babies.

Sacral dimple: Most of the time, sacral dimples are harmless and don't require any treatment. Rarely, a sacral dimple may indicate a serious underlying abnormality of the spine or spinal cord. To rule out any abnormality, your child's doctor may recommend an imaging test. If an abnormality is discovered, treatment depends on the underlying cause.

Maybe: A sacral dimple may be benign, but in newborns and infants, it may be associated with an underlying neural tube defect. In the newborn period, an ultrasound would be the standard imaging study. For older children, MRI may be indicated.