The unpardonable sin is the willful denial of Christ with deliberate forethought, the bible also calls it the sin unto death(1 John 5:16).
There is a need for us to know that not just any believer can commit this sin because there are certain requirements to be met by any believer who will commit this sin. A baby Christian cannot commit the unpardonable sin. There are Christians who are living in fear of having committed the unpardonable sin and some of them have had mental problems because of this issue but for the mere fact that it even crosses your mind that you’ve committed the unpardonable sin is a proof that you haven’t committed it at all.
So what are the criteria for committing the unpardonable sin?
Hebrews 6:4-6, “For It is impossible for those who were once ENLIGHTENED, and have TASTED OF THE HEAVENLY GIFT, and were MADE PARTAKERS OF THE HOLYGHOST, And have TASTED THE GOOD WORD OF GOD, and THE POWERS OF THE WORLD TO COME, IF THEY SHALL FALL AWAY, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.”
Now, it is good we analyze these verses one after the other for us to have a good grasp of what it is saying exactly.
According to the scripture above, to be ENLIGHTENED there means coming in contact with the message of salvation which gets a sinner convicted. Before anyone becomes saved, there is a spiritual enlightenment that precedes salvation.
TASTED OF THE HEAVENLY GIFT refers to salvation - receiving Jesus Christ as Savior. Salvation is the heavenly gift. John 3:16, Ephesians 2:8-9
MADE PARTAKERS OF THE HOLY GHOST refers to being baptized in the Holy Ghost with the evidence of speaking in tongues. Acts 1:5, 2:4
AND HAVE TASTED THE GOOD WORD OF GOD- To have tasted the good word of God refers to a high level of spiritual maturity. Those in this category have had some degree of spiritual growth and they fully understand the seriousness of denying Christ.  This cannot apply to baby Christians. They haven’t tasted the good word of God. Baby Christians are still on the ‘sincere milk of the Word (1Peter 2:2). Baby Christians cannot be guilty of this sin because they wouldn’t be mature enough to know what they are doing.
TASTED THE POWERS OF THE WORLD TO COME- the powers of the world to come are spiritual gifts. Someone that will commit the unpardonable sin must be someone that has experienced the spiritual gifts and walked in powerful dimensions of the anointing.
When you look at all these put together, it is clear and evident that a baby Christian cannot commit the unpardonable sin.