Thank you for providing such a thorough assessment of the symptoms. Your careful consideration of the potential causes of the nasal swelling is commendable and reflects a genuine concern for the child's well-being.

### Summary of Considerations:
The swelling of the nose in children can indeed arise from a variety of factors, including allergic reactions, infections, dermatological issues, or trauma, as you outlined. Each of these possibilities can carry different implications for treatment, and your approach to involving a medical professional for further evaluation is essential.

### Likely Diagnoses with Justifications:
- **Allergic Reactions:** This is common in children and can lead to localized swelling. Observing for other symptoms, like sneezing or itching, can help confirm this.
- **Infections:** Conditions such as sinusitis or localized skin infections (like cellulitis) can present with swelling and may require antibiotics.
- **Dermatological Issues:** Skin infections or inflammatory conditions can also cause swelling and may need topical treatments.
- **Trauma:** If the child has had an injury, this could explain localized swelling due to inflammation.

### Suggested Next Steps:
1. **Consultation:** As you mentioned, visiting a **General Practitioner (GP)** or a **Dermatologist** is a prudent next step. They will conduct a physical examination and may ask about accompanying symptoms to reach a diagnosis.
   
2. **Diagnostic Tests:** 
   - Allergy tests may be warranted if an allergic reaction is suspected.
   - Imaging studies (like a CT scan) can help visualize the sinuses or other structures if an infection or other issues are a concern.

3. **Treatment Plan:** The management plan will hinge on the diagnosis:
   - **Antihistamines** for allergic reactions, if appropriate.
   - **Antibiotics** if an infection is confirmed.
   - **Topical treatments** for any dermatological conditions.

### When to Seek Immediate Attention:
As you noted, any new or worsening symptoms, such as severe pain, redness, warmth, or difficulty breathing, are critical reasons to seek immediate care. 

Your proactive approach to addressing this issue is vital. It’s always better to be thorough when it comes to the health of a child. With the right guidance and care, I am hopeful that any underlying issues can be effectively managed. Please take care, and don’t hesitate to reach out for professional help. Your attention to detail and concern for well-being will surely aid in navigating this situation to a positive outcome.