The Wisconsin Water Library at UW Madison has STEM and Literacy Together Kits to use for story time. The kits include traditional storytime elements (reading, songs, art activity), along with a water-related STEM aspect.
Available for request:
Once Upon a Pond (all about ponds in Wisconsin) – Call no. 071246
Jump Around with Frogs (Wisconsin Native Frogs and Toad) – Call no. 281686)
Does it Sink or Float? (Buoyancy) – Call no. 232434
They are available to request here, though some sleuthing indicates they are not on the regular catalog.
If you are looking for some more great STEM (science, technology, engineering, and math) resources for younger kids, you might want to check out the Talk, Read and Sing about STEM Tip Sheets from Too Small To Fail. Or check out the IFLS Early Childhood Exploration Kits and School-age STEM kits (which you can reserve by sending an email to Leah at langby @ iflsweb.org)