The Bible does not directly address the modern concept of a child “picking” their gender identity, as this is a contemporary social and psychological idea. Instead, biblical teachings on gender and sexuality are based on the concept of a binary, created order.

Here is a summary of the key biblical perspectives and verses that are often cited in this discussion:

1. The Creation of Male and Female
The foundational belief for many Christians is that God created humanity as two distinct and complementary sexes, male and female. This is seen as a part of God’s original, “very good” creation.

Genesis 1:27: “So God created man in his own image, in the image of God he created him; male and female he created them.”

Genesis 5:2: “Male and female he created them, and he blessed them and named them Man when they were created.”

Explanation: These verses establish a clear duality of gender from the beginning of creation. The Hebrew word for “man” (adam) can be used to refer to both humanity in general and specifically to the male. The text highlights that both male and female are created in the image of God and that their distinction is fundamental to their identity.

2. The Duality of Marriage
Jesus himself affirms this creation account when discussing marriage, reinforcing the male-female binary as the basis for the marital union.

Matthew 19:4-6: “He answered, ‘Have you not read that he who created them from the beginning made them male and female, and said, ‘Therefore a man shall leave his father and his mother and hold fast to his wife, and the two shall become one flesh’? So they are no longer two but one flesh. What therefore God has joined together, let not man separate.'”

Explanation: Jesus’s reference to Genesis underscores the idea that the male and female distinction is not a social construct but a part of God’s design for humanity and the foundation for the “one flesh” union of marriage.

3. Condemnation of Cross-Dressing and Gender-Blurring
Some biblical passages are interpreted as condemning actions that intentionally blur the lines between male and female appearance and roles. These are often used in arguments against gender nonconformity.

Deuteronomy 22:5: “A woman shall not wear a man’s garment, nor shall a man put on a woman’s cloak, for whoever does these things is an abomination to the LORD your God.”

Explanation: This verse is often cited as a prohibition against cross-dressing. While the historical and cultural context of this law is debated, many biblical interpreters see it as a principle against the intentional blurring of the male-female distinction, which they believe is tied to pagan practices of the time.

4. The Unity of Body and Identity
Biblical teachings often present the body as an integral part of a person’s identity and a temple of the Holy Spirit. This view suggests that one’s physical body, including its biological sex, is a gift from God and should not be altered.

1 Corinthians 6:19-20: “Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price. So glorify God in your body.”

Explanation: This passage emphasizes that a person’s body belongs to God and should be used to honor Him. From this perspective, intentionally changing one’s sex would be seen as acting against God’s intended design.

Summary
The Bible’s message on duality concerning sex and gender is centered on the concept of creation. The prevailing interpretation among those who adhere to a literal understanding of the Bible is that God created two distinct and unchanging sexes, male and female, and that one’s gender identity is intrinsically linked to one’s biological sex. Therefore, the idea of a child choosing a sex different from the one they were born with is not supported by these traditional biblical interpretations.