I have an academic background in science (analytical chemistry). I'm disappointed that most of my fellow Americans don't have the foggiest idea what science is. They think that science is a collection of glorified fairy tales that has been voted upon by committees of 'experts'. They don't understand that science is a method for gaining knowledge about the natural world. One elegant experiment can trump thousands of 'experts'. To quote the late Nobel Laureate (physics), Richard Feynman,
"Science is the belief in the ignorance of experts."
That said, I don't think that First-graders or Second-graders are equipped to understand very much science, beyond interesting facts about animals.
I did an original kitchen chemistry experiment for my young niece and even younger nephew. It was fun for both of them, but my nephew did not have the foggiest idea about the bigger picture that I was trying to draw.
Yes, the general public definitely needs to know more about science. However I see no harm in delaying theoretical science--even at the most elementary level--until young minds have the readiness for it.