**Core Concept**
Diurnal enuresis and soiling of clothes in a 3-year-old child indicate a condition known as encopresis, which is a form of fecal incontinence. This condition is often associated with constipation, which can lead to a buildup of stool in the rectum, causing the child to leak or soiling of clothes.

**Why the Correct Answer is Right**
The treatment of encopresis involves addressing the underlying constipation. This can be achieved through a combination of dietary changes, increased fluid intake, and bowel management techniques. The use of laxatives or enemas may also be necessary to help soften and evacuate the stool from the rectum. In some cases, behavioral therapy may also be beneficial to address any emotional or psychological issues associated with the condition.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not address the underlying constipation that is causing the child's symptoms.
**Option B:** This option is incorrect because it only addresses the symptoms of diurnal enuresis and soiling, rather than treating the underlying condition.
**Option C:** This option is incorrect because it is not a suitable treatment for a 3-year-old child with encopresis.

**Clinical Pearl / High-Yield Fact**
The "Bristol Stool Scale" is a useful tool for assessing the consistency of stool and can help guide treatment for constipation and encopresis. The scale ranges from Type 1 (separate, hard lumps) to Type 7 (watery, no solid pieces).

**Correct Answer: D.**