**Core Concept**
Gonadotropin levels in infants and young children follow a specific pattern. Gonadotropins, including follicle-stimulating hormone (FSH) and luteinizing hormone (LH), are hormones produced by the pituitary gland that regulate the reproductive system. In the first few years of life, gonadotropin levels decrease significantly as the hypothalamic-pituitary-gonadal axis matures.

**Why the Correct Answer is Right**
Gonadotropin levels peak in the first few months of life and then decline to prepubertal levels by approximately 1-2 years of age. This decline is due to the maturation of the hypothalamic-pituitary-gonadal axis, which results in decreased production of gonadotropin-releasing hormone (GnRH) by the hypothalamus. The reduction in GnRH leads to decreased production of FSH and LH by the pituitary gland. By 1-2 years of age, gonadotropin levels have decreased to prepubertal levels, which are characteristic of the prepubertal state.

**Why Each Wrong Option is Incorrect**
**Option A:** 6 months to 1 year of age is incorrect because, although gonadotropin levels do begin to decline around this time, they do not reach prepubertal levels until later.
**Option C:** 2 years to 3 years of age is incorrect because gonadotropin levels have already decreased to prepubertal levels by this age, and there is little change in gonadotropin levels during this time period.
**Option D:** 3 years to 4 years of age is incorrect because gonadotropin levels have already decreased to prepubertal levels by this age, and there is little change in gonadotropin levels during this time period.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that gonadotropin levels follow a predictable pattern in infants and young children, and changes in these levels can be used to assess the maturation of the hypothalamic-pituitary-gonadal axis.

**✓ Correct Answer: B. 1 year to 2 years of age**