Some of the best tools for STEM learning all types of building tools. You can even use sticks from your back yard. Try using different types of building materials and include some magnets.  Tegu blocks (which are expensive) combine wooden block building with hidden magnets. Pick up some tinker toys at yard sales.  They are still some of the best building tools made. You can also have children take pictures of their buildings and draw them. Throw in a challenge by putting some pictures of really interesting buildings in the block area and encouraging them to build similar structures. Building is great because it really integrates Science, Technology, Engineering and Math. You can also check out the new Town Square module Technology for Family Child Care: Starting with a Child Centered Approach.  It talks discusses STEM.  Have fun