Play for early childhood development is critical but the nice thing is that there are also ways to integrate play and content in a lesson plan. I am not sure if pre k - 4 is age 4 or grade 4. Either way, there are great activities that can be staged that allow for critical scope and sequence. For example using sand, burying items, sifting (with larger items staying to the top and smaller things falling through), adding water, etc. are all science activities, while at the same time, offering an opportunity for sensory development (touch, smell, ...
This solution discusses outdoor play, exploration, and skill development are some of the important early childhood issues.