If you wanted to teach your child to read what would you do?
A) Spend time going over the ABC's/spelling, get age appropriate books, help them read through them, and read to you child.
B) Send them to the library once a week for an hour and hope they learned something.
C) Read to yourself, and hope they just happen to pick it up.
Kinda obvious that A is the best answer, but many parents teach about God by only doing B and/or C. You send your child to Sunday school once a week and/or go to Bible Study yourself and hope that somehow your child will just "pick up" information about God. This doesn't work. in most cases.
You need to actually teach about God. And someone made it easy! Family Time Training has a goal to help families train their kids from preschool up. They even have a free activity every month. Go check them out. Think of it as actually giving you child working ideas on how God works and how Jesus work.