With PBs, most editors want cover letters and the entire ms. Usually there are guidelines on their website.
Yes, look up the editor's name and use that in the cover letter. The letter for a PB is short and to the point. Polite though.
Something like this:
Dear (Editor's name):
(Attached/Below/Enclosed) is my 700 word picture book with the working title A Picture Book For Kids. I am submitting it to (publishing house) for possible publication.
Joey goes to the store to buy some bread, but instead, comes home with a reindeer. Not only that, but the reindeer talks.
Thank you for considering A Picture Book For Kids and I look forward to hearing from you. (Enclosed is a SASE for your response.)
Best regards,
A Writer
If it's nonfiction, and you have expertise in the field of the subject matter, you can state that in the third paragraph before your closing remarks.
