My name is Author TS and I'm writing to query about a toddlers' book I'd like to write. [A book you'd like to write? Is that as far as you've gone in this process? NB to US/UK readers: I am taking the Australian view of things, which is that you need to have a bloody good reason why you don't have sample material for a non-fiction submission.]
I'm a science communicator by trade, have been for the last fifteen years or so - working giving shows to all ages, leading interpretive walks and writing everything from press releases to tv show fact sheets to information signs. I'm currently on a mostly-break from work raising a toddler or two - and I'm finding that there's a dearth of useful and interesting science-y books for the 2-5 age range. So too are my nerdy parent friends. Everything's at the level of "junior science fact books" and that type of thing, which is immensely boring to a child who can't
themselves read yet but still wants an endless "Why?" of questions answered. [Okay, you've established your scientific (but not children's writing) credentials and the reason why you think it would be on a good project, but I'm still stuck on the fact that this is a nebulous project.]
So what I'd like to write is a simple short story (could be a one-off, could easily be one of a series if there was sufficient interest) that uses, relies on and very simply explains some science principle - a kind of detective or mystery story, if you like, where the science is what
solves the puzzle. Relatively simple language and broken up text, to suit illustrations on each page. The thing that would make this book particularly good is that at the back I'd put one or two "parents' pages", that explain the science principle in a straight-forward way that adults
can understand and then use to answer their kids' questions about it. Even if the adults in question haven't slept properly for more than a year :-). The parents' page/s would also include some possible things to try at home, simple ideas that let parents and kids try out some of the science for themselves without having to spend a lot of money on buying stuff. [Interesting ideas but, again, nebulous.]
I look forward to hearing from you as to whether this fits with any of the sorts of projects you are looking for. [Sorry, but you haven't given me anything that I can send to a publisher and unless you're already my client and/or have a well-established profile in this field, I simply don't have the time to shepherd you through the writing process, especially as you've never written for children before.]
Overall: this sounds like a request for a consultant, not a query letter. While the letter is nicely constructed, you can't send out a query for a project that is nothing more than an idea - well, you can, but don't expect an overwhelming response. At least have a plan that you can send the agent.
What you haven't mentioned: um ... see above.