Ah, gotcha! When I want to know what the science standards are in my state for certain grades, I google the Dept of Elem Ed and look at their science curriculum. BUT (easier?) if you can find NF books for kids at your library that cover your topic or similar topics in the age range your ms targets, then I'm betting you're on solid ground.
As to the pitch, I'm not sure you need to be super-specific for publishers; usually "Ages: 4-8" works for most PBs.