**Core Concept**
The child presents with a smooth-surfaced bluish lesion associated with an erupting tooth, which suggests a soft tissue reaction to the tooth. This condition is characterized by an abnormal proliferation of fibrous tissue in response to the presence of a developing tooth.

**Why the Correct Answer is Right**
The lesion is likely a _**Gum Eruption Cyst (GEC)**_, also known as a _**Gum Eruption Cyst or Bohn's Cyst**_. This condition occurs when the dental follicle, a fibrous tissue surrounding the developing tooth, becomes trapped between the tooth and the surrounding bone. The trapped follicle can accumulate fluid and form a cystic structure. The bluish appearance is due to the presence of fluid within the cyst. The radiographic examination reveals a soft tissue shadow, indicating the cystic structure. The absence of bone involvement is consistent with GEC, which typically does not involve the surrounding bone.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a _**Gingival Cyst of the Newborn**_ is a rare, congenital condition that occurs in infants, not in toddlers.
**Option B:** This option is incorrect because a _**Gingival Fibroma**_ is a benign tumor of the gingiva, which is a firm, sessile mass, not a bluish, cystic lesion.
**Option C:** This option is incorrect because a _**Rathke's Cleft Cyst**_ is a rare, congenital cystic lesion of the anterior maxilla, not associated with an erupting tooth.

**Clinical Pearl / High-Yield Fact**
A key feature of GEC is its association with erupting teeth, particularly in the primary dentition. This condition is often asymptomatic and resolves spontaneously as the tooth erupts.

**Correct Answer: D. Gingival Eruption Cyst (GEC)**