"How do we know there were giants?" my eldest daughter asked, out of the blue.
"Are we talking Jack and Beanstalk or the Bible?"
The other one chimed in, "Because the Bible's God's word."
"I think what she's really asking is, 'Why do we believe the Bible is God's word?'
"We verify the things that we can. If those things stand up to scrutiny, we can trust the things we can't verify."
My youngest's approach is unfortunately common. She seemed scandalized the older one even asked such a question and wanted to take the "God said it, I believe it" approach.
I want them to know, though, that we don't take the Bible on blind faith. It's a reasoned faith, a trust in a trustworthy source.
We will never be able to verify every line of the Bible. But every year or so we find more reason to trust it. "The Hittites didn't exist." Oh, wait, yes they did. "There was no written language in Canaan during the bronze age." Yes, there very much was. "There was no King David." "Solomon didn't rule as much as the Bible claims." "Israel wasn't a powerful kingdom." The objections keep getting knocked down. And that's just the Old Testament. The NT case is much tighter.
Does this prove there were people two or three feet taller than what would consider "tall?" No. But if the records are reliable everywhere else, we have no good reason to doubt and every reason to accept the account.