As a parent and grand parent I've learned exactly what that was about. The very young tend to believe other people so innocently, quickly, and happily, like about Santa and the reindeer. My youngest daughter was at last allowed to go play in the back yard, bounded by a gold course. She saw golf balls everywhere in the yard, new ones daily, but didn't bother them. One day she asked what they were. Playfully I said "Do you suppose they are goff eggs laid by a goff bird?" She didn't reply. While preparing for mowing by picking up the golf balls I noticed perfectly constructed bird nests around the yard full of golf balls. I realized she had believed me literally, so I corrected that little myth, and was very careful from that day to teach only truth to kids, with no messing with facts.
As we get older we tend to learn to argue some or a lot when hearing something abstract, like 'the blood of Jesus washes us white as snow'. Adults pick up bad habits, doubting things not seen in nature, so we have a lot harder time living by faith; best done by trusting God like a little child eager to learn.
I would doubt there would be much surprise, for those who know they need to be, [with God's help], become. Those who never realize the need are not likely to ever be there at all. Of course that is only the way I see it.