Hunter has always believed in aliens. Melody thinks he's crazy. But when their teacher disappears in the middle of the desert, the two kids must learn to trust each other as they race to rescue her from the sinister forces holding her captive. [Good hook, well expressed.]
And the closer they get to the truth, the more questions they uncover. Was Miss Pepper really abducted by a flying saucer? [Aren't flying saucers a bit 1977?] Why are they being chased by commandos and black helicopters? What does Mr Burgundy, the sinister government agent, know about the disappearance of Hunter's father four years ago? And how come aliens never wear pants? [Nicely paced, and it hooks me into the story - I want to know about the pants now!]
ENCOUNTER AT SHADOW ROCK is the first in the Hunter Black series of science fiction adventures for independent readers aged 8 to 12, and is complete at 22,500 words.
With an action and mystery vibe that's like "Spy Kids" meets "The X-Files" [important you said it's 'like' these things not that it 'is' these things - the first word gives us content, but using the second would have be worrying that you're thinking only of the film deal], the series will see Hunter and Melody investigate a variety of strange and eerie cases, as the mystery surrounding Hunter's father and his involvement in the global alien conspiracy gradually unfolds.
I have seven years of experience as a technical writer and publications manager, and my short story "The Boy Who Believed in Dragons" was published in AUREALIS magazine. [Why have you decided to write for children?]
Thank you for your time and consideration.
Overall: a very good letter. As the story is 22 500 words long, you don't have to give as much detail for the story, so this is an appropriate amount of words to get an agent/publisher intrigued.
What you haven't mentioned: why you're writing for children. As previously mentioned, children's publishing is its own little world and you will need to establish some bona fides - maybe refer to some titles you've read that you really like and that are in the same genre.