Moderate to conservative scholars have penned many excellent defenses of the historicity of the Gospels. Even more liberal scholars like Dale Allison often make useful point in their defense.
There is, however, a neglected line of evidence for the historicity of the Gospels–and that's what they don't say. Mark says nothing about the childhood of Jesus. John relates in passing a scurrilous rumor about his illegitimacy. Both Matthew and Luke contain infancy narratives. Luke records one incident from his boyhood. And that's it!
Yet many readers would naturally be curious to know more about his childhood. If the Gospels were fictional biographies, we'd expect them to satisfy their pious curiosity.
To take a comparison, stories about superheroes like Batman, Spiderman, and Superman contain detailed backstories regarding their childhood. And that's because fictional writers aren't constrained by factual knowledge or hard reality.
The obvious reason the Gospel writers say so little about the childhood of Jesus is because they only write about what they know, and they don't know much about his childhood. And when you ponder that, it's very realistic.
Most famous people, unless they are born into a famous family, aren't born famous. Nothing is written about them before they become famous. Very few people ever heard of them before they become famous.
And oftentimes, what's written about them has reference to the things they did after they become famous. To the things that made them famous. What they did before they became public figures may get far less attention. And depending on the time and place, far less material may be available.
If you knew ahead of time that they were going to become famous, you could interview neighbors, older relatives, &c. But by the time they become famous, the pool of information about their childhood is already beginning to dry up. By the time biographers or historians write about them, living witnesses from their youth may be few.
To take another comparison, although the resurrection of Christ is a central event, both in the Gospels and the NT generally, nowhere is the actual event described. No NT writer describes the scene of Jesus coming back to life in the tomb.
Instead, they describe his death. His entombment. And the effect of his resurrection: his post-Resurrection appearances.
Why don't they record the event itself? For the simple reason that they only report what they know. No one else was in the tomb with Jesus when he came back to life. And even if someone had been there, there's a sense in which there was nothing to see, because it was dark inside the tomb.
Now, if the Gospels were fictional biographies, we'd expect them to show the Resurrection. Give a visual description. They don't do that because the Gospel writers are constrained by the factual information at their disposal. By personal observation or testimony from eyewitnesses. But Jesus was alone in the tomb.
In the Gospels, what you get is what was seen. There's a lot you don't get because there's a lot that no one saw by the time of Christ's public ministry.