Isaw three kids sitting on the porch across the street. where does the comma go

Hey there! Hello!

I believe the comma should go here:

"I saw three kids sitting on the porch, across the street."

"Across the street" is a sentence fragment. These are typically separated from the rest of the sentence with a comma. Sentence fragments may seem like sentences, but you couldn't make it it's own sentence, since it doesn't contain a verb. A sentence must have a verb and a subject in order to be considered valid, and in the case of fragments, they're purely there to add more to the current sentence. 

I hope this helped you out! Feel free to ask me any additional questions if you have any. :-)

I think that the comma goes like this ''I saw three kids sitting on the porch across the street"