Step 1: Understanding the background.
Gautama Buddha, the founder of Buddhism, was born as a prince in Lumbini (in present-day Nepal). Before he renounced worldly life, his childhood/early name was Siddhartha.
Step 2: Analyze the options.
(A) Sidha: Incorrect — not historically correct.
(B) Sadhu: Incorrect — a sadhu means a monk or saint, not Buddha’s childhood name.
(C) Siddhartha: Correct — Gautama Buddha’s early name was Siddhartha.
(D) Sidharth: Incorrect — a misspelling/variation of the correct name.
Step 3: Conclusion.
Thus, the correct answer is (C) Siddhartha.