How exciting! Students love learning about science so you'll have lots of fun.
I always think the best place to start is with the standards - what is it that you want the students to learn? I see that you're working with elementary so my suggestion would be to enhance and engage the students through the use of picture books. Are you familiar with NSTA's publication, Science & Children? Each month Christine Anne Royce features a column, Teaching Through Trade Books. In it she focuses on lessons and engaging investigations and activities that are inspired by children's literature. The lessons are structured using the 5Es Instructional Model and aligned to NGSS (even if you aren't in an NGSS state, the lessons can still be aligned perfectly to any state science standards). The lessons are also differentiated for lower and intermediate elementary.
Here is an example from one of my favorite lessons Will it Sink or Will it Float? http://static.nsta.org/files/sc1409_18.pdf
In this lesson students investigate structure and properties of matter.
There are many great lessons to choose from so if you need any help looking for a particular concept let me know.
I hope that helps you more with planning.