**Core Concept**
The child's presentation of tingling and numbness in the ulnar side of the finger 4 years after an elbow fracture is due to a complication of the initial injury. This is related to the growth and development of the bone, leading to a deformity that affects the surrounding nerves.

**Why the Correct Answer is Right**
The ulnar nerve runs close to the lateral condyle of the humerus. A fracture of the lateral condyle in a child can lead to a nonunion or malunion, resulting in a cubitus varus deformity. This deformity can cause the ulnar nerve to become stretched or compressed, leading to symptoms such as tingling and numbness in the ulnar side of the finger. The cubitus varus deformity occurs because the medial epicondyle grows more than the lateral epicondyle, causing the elbow to twist inward.

**Why Each Wrong Option is Incorrect**
**Option A:** A supracondylar fracture of the humerus can lead to complications such as compartment syndrome or nerve damage, but it is less likely to cause a cubitus varus deformity and subsequent ulnar nerve compression.

**Option C:** An olecranon fracture would typically affect the triceps tendon and the posterior aspect of the elbow, rather than the ulnar nerve.

**Option D:** Elbow dislocation would cause more immediate and severe symptoms, including pain, swelling, and limited mobility, rather than delayed onset of numbness and tingling.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize that children's bones are still growing, and fractures can lead to complications due to growth and development. A high index of suspicion for nerve compression and deformity is necessary in children with a history of fractures.

**✓ Correct Answer: B. lateral condylar humerus**