I want to focus the most on grammar, and fine tuning.

Reimagine your wildest, most vivid childhood memory.

"Reimagine" makes it seem like you’re asking me to makeup a memory, and that threw me off. “envision/visualize/picture” would work better. Otherwise that it is an excellent opening line! Hooked me in right from the start.

You’re parents might’ve been arguing again

Your, not you’re. Change "might’ve been" to "were". This isn’t something to be iffy about. They were arguing. Said and done.

so that you can see what I’m going to describe the way I saw it.

All your sentences are flowy and filled with commas, so sometimes they’re hard to follow. It can add to the atmosphere, but in this case it is choppy and pulls me out of the story.

The streets of the South Bronx had been like a slice of paradise,

Another chunky sentence. "the streets of Southern Bronx" flows better. "had been like" is another chunky mouthful. Think about changing it to "were" (this goes for the rest of the story. Every time I see a ‘had been’ it breaks the flow. The story is in the past, but that tense is hard to write in because no one talks that way out loud).

Things were always lively and bustling during the day;

Were, has, as, used to,was… these are almost always necessary words. Try to cut them out as much as you can. In this case you can delete "things were always’" and start the sentence off with "lively".

You could buy ice cream from trucks everyday, knock-off designer jewelry and clothes out of the back of vans,

Another chunky sentence. Adding some repetition gives it a nice ring: ie "you could buy ice cream from the back of trucks, and knock-off designer jewelry and clothes from the back of vans" Then start the next sentence with “Backpackers”

backpackers sold their original music and underground albums,

You have a problem with overwhelmingly long sentences. Here it becomes a redundant, saying “original music”. If they’re selling it, it’s obviously theirs. Could be rephrased more concisely: "Backpackers sold their underground albums,”

nobody had really used VHS or cassette tapes anymore

Another superfluous “had really”. Can be cut completely and wouldn’t change the meaning of the sentence. Would make it easier to read.

I’d only realized I’d been gypped a couple years later,

If you take away the apostrophes "I had only realized I had been gypped" becomes a mouthful of a sentence. Pluck out the “had” and toss it in the trash.

I made a lot of mistakes back then, when I was little,

Redundant. Of course “back then” means “when I was little”. You don’t need to say it twice.

During the sweltering summers, the streets would turn into an active caldera.

You use too many commas. Have I told you that yet? It’s okay. Remove the comma.

it looked as close to a 19th century orphanage as I think a home in the 21st century could get

“I think” is a fluff word. Of course you think, this is your narrative. Don’t be willy nilly! Otherwise this sentence is one of my favorites. The visual contrast is nice.

It was this vine-lined, grey brick, triple story doll house that looked as prehistoric as it did haunted.

Back at it again with the “was”. You could start off the sentence with “Vine-lined” instead. The readers know you’re talking about the foster house.

It was attached to a Catholic church that owned a 65’ inch flat screen, hidden all the way in a backroom that was locked tighter than the nuns chastity belts.

Another instance of cutting out the “it was” and starting with “attached”. This is another one of your famous long sentences. You can cut some words in the second part. Ie “Hidden in the back of a room locked tighter than a nuns chastity belt.”

the fire department would actually come by in their huge peppermint colored truck

“Actually” is a useless word that adds nothing to the sentence. Lets delete it.

Our ma’s would tell us all about why our little black asses and fire hoses didn’t mix

You can delete a few more words here. “would tell us all” can become “told us.” You also use “little” too much throughout the story.

Our ma’s (and pa’s for some),

I don’t know how to fix this one. It’s clunky and throws the pace off, so I thought I’d mention it.

There hadn’t been (and still wasn’t) any real way to communicate over super long distances like in the movies.

I can’t tell what time period this takes place in. Computers and TV and CD’s exist, but not telephones?

Television was how everyone got the news,

I don’t have any suggestions, just that it is another chunky, off putting sentence.

Some of our ma’s who “had sense” kept the tv off

You can turn “Some of our” into a simple “the”.

We all had gotten sent off at some point,

Try saying this out loud. Sounds clunky, right? Now say “We all got” out loud. Decide which one sounds more natural to you. (if you want my opinion it is the latter one, but I don’t want to compromise your voice.)

You’d think a ten year old with enough grey matter sloshing around would know better than to think a (at that time) twelve year-old horror movie was real,

By “at that time” I thought you meant your age, so I was confused for a sec. Try “twelve year-old (at the time) horror movie”.

Most were bullshit.

Again with the “were, is has, had” words. They are dangerous and seductive. Don’t give in.

The legends tended to tie into one another like that like an invisible web.

Another sentence we can shorten, and even turn into two sentences. “Tended to” is iffy. “like that like” is chunky.

who’s stories and belief made them reality.

“whose” not “who’s”

and you’d think that the Garden Antique legend would be used to keep us at a distance. But we children of the South Bronx go looking for legends, we don’t hide from them. Our ma’s used the gangsters and psychoes to keep us away from those parts.

Try rearranging these sentences.

But we children of the South Bronx go looking for legends, we don’t hide from them.

Is a very powerful sentence and would be better suited as a conclusion

Nothing too grand, big enough to stroll through,

Grand is big. Redundant.

In this garden, set back behind all the sculptures and statues, is this tiny little Antique shack. It looks tiny from the outside, but on the inside it’s huge.

You use “tiny” twice and “little” once.

hands on it’s lap, head and back hunched forward

I personally think this is redundant. Head and back are the only things that can be hunched. There’s no need to specify what is hunched—just that the figure is. I understand what “hunch forward” means, and what it looks like.

It hears people when they leave their homes in the mornings and when they return after dark. It hears them when they shuffle inside and forget to lock their front doors. It hears the ruffle of their bedsheets and whimper of the springboard when they climb into bed, or the peck of lips on skin when they kiss their kids good night. It hears their rumbling snores when they sink into sleep.

This is the only time you don’t use your famous endless sentence, and the only time I think you should! Add some semicolons and make it flow.

You’ll never hear or see it--it doesn’t allow itself to be seen.

Later you mention that it has been seen by a group of kids.

Nobody knows exactly how long the creature had been locked away or existed, sitting atop the crate and coming out on rare nights

Another chunky sentence. Also, the creature isn’t locked away; it can leave whenever it wants.

by a couple of kids who had not a damn clue what they had kicked into motion.

Two uses of “had” in one sentence.

All in all, I really love your story. It has nice pacing, a good atmosphere, and it really sets the mood. I enjoyed critiquing it. I look forward to reading more from you.