I am currently reading "Mindstorms," by Seymour Papert, which is the namesake of the LEGO product for building intermediate robotics. The concepts of that product and its language—LEGO/LOGO—are inspired by Mr. Papert's work therein. Read it. Let's compare notes afterward, because I'm afraid that your questions betray your all-too-easy view of "education." To the questions:

1. "What coding languages should be considered?" All language; specifically (unto each child), the language that child uses—primarily—in communicating outside of that person's self. Around these parts, that's most usually English or American Sign Language (or, perhaps, Signed English). Start out with epistemology: be up-front and honest (if you are willing to do this) that the class is going to be primarily a safe place to—as an undercurrent to the purpose of attendance—think about thinking ("metacognition.") Speaking of that "purpose of attendance": it sounds as if you want to simply check off some tacky ticky boxes on a form to "certify" that the children have "done the work." To each one, ensure that person has a reason for being there, because you owe each a personalized curriculum. If they are required to be there (compulsory attendance), it's spoiled and can't be considered true "learning" (which is *always,* I contend, autodidactic).
2. I recommend LOGO, particularly because it has a "body-syntonic" application. This ensures you (and others who use it) may surmount the "nerds vs. jocks" stereotyping that could happen, often portrayed in popular media in the LOGO age.
3. If you must indoctrinate "the class" to a particular language, use LOGO. Use the "get up and walk around and figure out how *you* think about walking a circle, then write it down" type of lesson plan, the subroutine instructions that build up into a palette of useful examples of geometry, and the opportunities for functionalization. It's also a good foundation, I've decided, for having folks think in a slightly less-absurd way about points, lines, curves, and positions, because the Turtle (cursor/caret) has *direction,* as well as position, and is therefore more vector-y (i.e., real-world applicable) than simple point-based systems-"frozen"-in-time.
4. "Are there are any self-guided coding websites that can be used by children to learn coding using guidance and help online?" With this, you make it known that you're not really willing to develop. Read a book. Or do you want a "teach children to use a self-guided coding website" website to help you? I don't ask it to be rude, but to help you gain an enthusiasm for the position of being entrusted with young learners. If going down that road, instead of having each come up with (a) what learning is, (b) where learning comes from, and (c) when to learn (i.e., a reason for learning) as the first day activities, just know that the children (as a whole and each, individually) aren't stupid (don't label them such, even in your thoughts), and any misconceptions they garner from substandard, non-individually-catered learning materials will be on your head.

As an on-the-outskirts "hipster," I understand this as a glimpse into the future, where we've learned from the mistakes of the digital age. Though digital's "always-on," "always-streaming" (as private electronic storage of music has become passé) form is good for those who want a "quick hit" of a Top 40 "quick hit," we've lost the listening experience of the "art of the album" -- not to mention actual "album art," which represents a hold-in-one's-hands physical artefact: a manifestation of music, made real. It means more to buy a physical album. Some of us have found this to be true with dead-trees-type books, already.