Problem: "People get married because they love eachother" is an over simplification; a child's view of mariage. "People get married to start a family" is a more correct, tho still child-appropriate, answer. To explain this would require the parent to define the different types of love, which might not be appropriate for a 3-4 year old.
Long ago someone asked why many clergy approved of homosexuality. Have you read 2nd Timothy? "3 For the time is coming when people will not endure sound teaching, but having itching ears they will accumulate for themselves teachers to suit their own passions, 4 and will turn away from listening to the truth and wander off into myths." - 2 Timothy 4:3-4 Now there's little context in the letter itself; we must rely on the rest of the Bible to provide context, to determine what sound doctrine is. What does the Bible say about sexual sin? About marriage? What examples does it give of each?
There was some debate in the early church about how much sway the Mosaic law should hold over Christians. I you want to read the church's decision, it's in Acts 15. There's some debating there which leads up to this letter:
"The apostles, the elders, and the brethren,
To the brethren who are of the Gentiles in Antioch, Syria, and Cilicia:
Greetings.
24 Since we have heard that some who went out from us have troubled you with words, unsettling your souls, [h]saying, “You must be circumcised and keep the law”—to whom we gave no such commandment— 25 it seemed good to us, being assembled with one [i]accord, to send chosen men to you with our beloved Barnabas and Paul, 26 men who have risked their lives for the name of our Lord Jesus Christ. 27 We have therefore sent Judas and Silas, who will also report the same things by word of mouth. 28 For it seemed good to the Holy Spirit, and to us, to lay upon you no greater burden than these necessary things: 29 that you abstain from things offered to idols, from blood, from things strangled, and from sexual[j] immorality. If you keep yourselves from these, you will do well.
Farewell."
Christians do take the Old Testament to be an example, so the definition of sexual sin still applies, but the specific punishments & sacraments are removed, as are other laws about washing, eating certain foods, etc.
And the apostles various letters add in things about meeting together, taking the Lord's supper, not stealing, deceiving, etc.