The following approach has been very helpful to me in working with young people who seem not quite mature enough to obey the gospel.

The first thing to do when a child shows interest in baptism is to praise and encourage them for taking an interest in God and in the things that he teaches us.

Secondly, ask them to explain to you as best they can, why they want to be baptized.  What you must assess from their answer and your familiarity with them, is their ability to comprehend sin.  One of the best markers for this is an overburdening sense of guilt.  Every youngster will come to an academic or intellectual understanding of sin before they internalize a sense of responsibility for their own.  Have they come to a point where their conscience is consistently troubling them?

Have them read Matthew 18:1-3 with you.  Ask, “What question did Jesus’ disciples ask him?”  Guide your child to understand that the disciples wanted Jesus to tell them who was greatest in the kingdom of heaven.  Then help them see that Jesus used a child as an example of what everyone must become to enter the kingdom of God.  Help them also understand that Jesus would not do this if children were lost sinners.

Have them read Matthew 19:13-14 with you.  Ask your child, “To whom did Jesus say the kingdom of heaven belonged?”  Guide them to see that he said it belonged to children and those who were like children.  Once again, impress on their minds that Jesus could not have said this if children were held responsible for sin.

Once they see Jesus’ point about children, you can ask them if they believe that they are still a child in God’s eyes.  A good way I have found to do this is to offer them an answer on a scale of one to ten, one being an infant and ten being an adult.  Ask them where they see themselves on that scale, and of course it will be somewhere under the “ten” mark.  This usually helps them to see that they are not yet old enough to be held accountable for sin.

Another idea is to use a younger sibling, or any much younger child or toddler with whom they are familiar.  Ask them if their parents hold this little one accountable to the same standard as adults.  In my experience, this illustration has never failed to help youngsters see that God, like parents, does not consider us to be “sinful” until we have reached a particular level of understanding and maturity.

The above approach helps make it fairly easy to comfort a “too young” child with the idea that they can wait, while at the same time reinforcing and encouraging their inclination towards obeying the gospel.  Taking the time to go through this brief study with them will give you insight into how much truth they comprehend and are internalizing and therefore how close they are to needing to obey.