Oh really?
The word "doctrine" simply means teaching.
Let's see what this thief knew both about Christ and any other Christian teachings:
39One of the criminals who hung there hurled insults at him: "Aren't you the Christ? Save yourself and us!"
40But the other criminal rebuked him. "Don't you fear God," he said, "since you are under the same sentence? 41We are punished justly, for we are getting what our deeds deserve. But this man has done nothing wrong."
42Then he said, "Jesus, remember me when you come into your kingdom." (Luke 23:39-42)
So what had this thief learned already?
* He knew Jesus was perfect -- or at least perfect in His public life (v. 41). (How many contemporaries with access to Bibles still don't recognize that?)
* He feared God (v. 40), and knew that was proper. (How many contemporaries lack a fear of God?)
* He knew the one of the commandments enough to know he was guilty and was received due punishment. (v.41) (How many contemporaries play down steading as if it was nothing -- and here he said it was worth the death penalty!)
* He knew enough "teaching" about Jesus that He was both trustworthy (somebody of ultimate authority He could appeal to about the most important thing in life -- God's Kingdom) -- v. 42...
* ...and, as such, He knew Jesus was the Living Way into a true Kingdom entrance [How many even on these FReeper threads have chastised us in the past week for claiming Jesus is the Only Way to heaven?]
I'd say this guy knew a fair enough. In fact, even the other thief heard of Jesus' "savior" status!!!
Little children do not understand doctrine, and yet Jesus says we should be like them (in the sense of trusting Him) if we want to enter the Kingdom of God. (Matt. 18)
They don't? You're telling me that little children don't understand some basic doctrines about, say, prayer?
Or what it is to trust?
I think you simply forgot to put an adjective by "doctrine" -- like "in-depth."
Unfortunately for your argument, Christian doctrine simplydid not exist yet. Yes, the thief knew the real score. "Doctrine" didn't exist until long after the thief had joined Jesus in heaven.
The lesson: churches can be pretty arrogant, sometimes -- assuming that salvation only comes through the teaching of the church.