I wish I could teach science at any grade level- I deeply enjoy the subject myself.
I don't think that second grade needs a formal text or anything like that for science. It might be better for children to just explore for now, and focus on sharpening their skills in math, reading, and writing.
Some ideas for kids that age (well, I've been out of 2nd grade for 12 years now!): take them to a farm to watch a calf or lamb or other baby get born, and explain the process, go herping or birdwatching (buy the field guides and identify species), dissecting organs or plants and make posters about the structure in an age-appropriate way, make a simple wiring project on a board with a doorbell or lightbulb, etc. They love to do things at that age. And take advantage of their natural curiosity and teach on the spot. I've had a lot of fun explaining DNA and biochemical concepts to little children using age-appropriate terms. They are little sponges and definitely understand more than we give them credit for.