**Core Concept**
Proptosis, or exophthalmos, refers to the forward protrusion of the eyeball from the orbit. This condition can result from various causes, including neoplastic processes. In pediatric patients, certain tumors can cause proptosis due to their location and potential for orbital invasion.

**Why the Correct Answer is Right**
Proptosis can be caused by tumors that arise from or metastasize to the orbit, eyelids, or surrounding tissues. Neuroblastoma, a malignancy of the sympathetic nervous system, can present with proptosis due to its tendency to spread to the orbit and eyelids. Ewing's sarcoma, a primary bone malignancy, can also cause proptosis by invading the orbit or metastasizing to the surrounding tissues. Nephroblastoma, a type of kidney cancer, can metastasize to the orbit and cause proptosis. The combination of these factors makes all three options correct.

**Why Each Wrong Option is Incorrect**
* **Option A:** Nephroblastoma is less commonly associated with proptosis compared to the other options. However, it can metastasize to the orbit and cause this symptom.
* **Option B:** While neuroblastoma is indeed a correct answer, this option does not acknowledge the other two correct options. Therefore, it is not the best answer choice.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with proptosis, it is essential to consider the possibility of a neoplastic process. A thorough head and neck examination, including evaluation of the orbits and eyelids, is crucial in identifying potential tumor sites.

**Correct Answer Line**
✓ Correct Answer: D. All of the above