Preschool children at church: Sunday school curriculum
When I taught Sunday school, the church provided the curriculum. At the church I attended in Nova Scotia, I believe they used Baptist Press materials. At the next church, I cannot remember if I provided it or if they did.
I loved the felt materials for telling Bible stories when I was a child because the visual helped me remember the story. They are more pricey but I think worth it if it is going to be used over and over again.
We have coloring books for the Lord's Prayer, the Armor of God and one other one too, which are good teaching tools.