Faith is the most important quality a Sunday School teacher can instill upon a child. It is the basis for his spiritual growth. Without faith, no other teaching will benefit a kid in the short term. Faith in God is the seed that must be planted and established as the foundation, then that faith of the child will be ready to grow.
Here is a list of Bible verses on faith that can be used to teach children on the topic of faith.
Now faith is the assurance of things hoped for and the evidence of things not seen.
But without faith it is impossible to please God. For whomever comes to God must believe He is, and he rewards those that diligently seek Him.
For by grace are you saved through faith, it is not of your own doing: it is the gift of God, not a result of works, so that no one can boast.
For we walk by faith not by sight.
So then faith comes by hearing, and hearing by the Word of God.
If you have faith the size of a mustard seed nothing will be impossible for you.