Matthew 18:1-6 (ESV)
At that time the disciples came to Jesus, saying, "Who is the greatest in the kingdom of heaven?"  And calling to him a child, he put him in the midst of them  and said, "Truly, I say to you, unless you turn and become like children, you will never enter the kingdom of heaven.  Whoever humbles himself like this child is the greatest in the kingdom of heaven.
 "Whoever receives one such child in my name receives me,  but whoever causes one of these little ones who believe in me to sin, it would be better for him to have a great millstone fastened around his neck and to be drowned in the depth of the sea.
What does it mean to cause a little one to sin? I suppose it could mean many a thing. But one is led by the use of the language opposite believe and the word scandolon in the Greek, from which we get scandal, Jesus means causing these little ones to first doubt Christ’s word, and then to doubt Christ. To lead them into unbelief. Children and little children tend to be much more open to faith in God than jaded adults. But a good majority of those calling themselves Christians in the united states don’t believe this. They confuse faith with mental assent, repentance, and obedience to God’s law, things they do. The nature of faith is really as deep a mystery as the Trinity.
It isn’t to say that as self aware adults, or even as little children there isn’t an aspect of faith that is grounded in our doing, It is just what we are responsible for in faith is not the sum total of what it means to believe. If faith were an iceberg, that aspect of faith we are conscious of wouldn’t even be the whole of that which is exposed to view. Faith, at least where it comes to God, is much deeper than even what we are conscious of. To be sure, self aware adults, adolescents and so forth will be aware of their faith, but this does not mean one has to be aware of it to have it.
The primary operator in faith is always the Holy Spirit who works through the gospel and sacraments to create faith, without whom faith is impossible in all its forms. But the little ones can believe in Jesus because of the work of the Holy Spirit. This is why we baptize them. Jesus says they do believe him.
This is where I think most are guilty of causing the little ones to sin. They bring them up to confuse faith with their own doing. They bring them up to despise baptism as a nothing that is not needed except as a pledge of obedience. They bring them up to ignore the promises of God, and in effect make baptism their own work. They themselves often refuse to even investigate what scripture has to say concerning baptism. Of course, this need not be limited to baptists, small b, but all those who teach contrary to the word of God and drive people to despair and self righteousness. There is a millstone waiting.
It is a shameful thing to act as if children can’t believe, when Jesus so clearly says they do. The real miracle is not that children believe, but that adults do.