This one gets a negative reaction from me. From a technical point of view, it is quite lacking. Essentially, it's one long action sequence - which is fine - but I did not find any of the action handled well. From weird perspective wobbles ("they ran toward them" - how about they ran toward her?); to inappropriate digressions (her uncle, the captain - I thought this was tense?); to out-and-out errors (the "mutie" grabbed her arm - yet she dodged it? Don't you mean grabbed AT her arm?) - it was just amatuerish in feeling.
Plot wise, it was weak. Girl finds MacGuffin, narrator withholds information about MacGuffin to build false tension, girl is rescued by versimillitude shatteringly friendly Deus Ex Machina (the "Dead Boys" gang who, unlike the others, are chivalrous for some reason?). Final revelation is that the heretofore purposely undescribed MacGuffin turns out to be useless - a bad way of manufacturing false tension and a good way to leave the reader feeling cheated. In my opinion, it would have been a stronger story had it opened with the girl taking the cereal from the shelf and describing it. She may not have known what it was, but the readers would have.
See Robert Bloch's "Notebook Found in a Deserted House" for a good way to use the uninformed perspective of a child to instill horror in the reader. He may lack the worldly knowledge to know it's a trap - but we do not. So we cannot help but feel the dread he does not. That could have worked with this story too.
I have a real personal dislike of the speculative fiction story which leaves itself intentionally vague. It opens with a vague train of thought about a vague item needed for a vague purpose for a vague little boy. In speculative fiction especially, directness is called for. The story will stand if you tell it well, regardless. Some people call the vague approach "immersive" - I regard it as a good way to make sci-fi and fantasy inaccessable and confusing to most audiances.
Finally, I want to remark that this story brings absolutely nothing original to the table. It's essentially a total remake of "The Underdweller" by William F. Nolan (1957). A disaster has killed all adults, leaving the world run by children. This concept was famously re-used in the ST:TOS episode "Miri" (1966). All of those things, of course, are based on their granddaddy "The Lord of the Flies" (1954). To say this is well-worn ground is an understatement.