So I found The World the Children Made in the Sept issue of Saturday Evening Post, and now I have a new question about what is also called The Veldt. Is there any way I can find out when he wrote the story? And if he had anyone read it before it was published? Also, maybe if it was written in a smaller journal before that? Thank you!

http://www.fantasticfiction.co.uk/authors/Ray_Bradbury.htm
Lists "The Veldt" with a 1950 publication date. My Illustrated Man copy credits the Curtis Publishing Co. also with a 1950 date. The IM collection was first in print in 1951.
As for "Who" may have read the s.s. before it's publication - !?!

Although Ray has described in interviews his inspiration for writing "The Veldt"--typing the words "The Playroom" on a piece of paper--I don't remember him mentioning a specific date. Sometimes he keeps lists of such words for years ("Trapdoor" and "At the End of the Ninth Year" being good examples) but the way "The Veldt" just flowed out it's safe to assume there wasn't a long delay between writing and publication. It's also QUITE safe to assume it didn't appear first in a smaller journal, for these reasons: 1. Bill Nolan and Donn Albright would have found and noted it. 2. Writers (or agents, and he'd had his agent for several years by then) always send stories to the high-profile, high-paying markets first. Once the "Saturday Evening Post" has accepted the story, no need to submit elsewhere. In 1950 Bradbury was just beginning to become famous and was two or three years from making any real money, so he'd have an incentive to see as much in print as soon as possible. His wife, Maggie, usually reads his work pre-publication. In 1950 they had one daughter and by the end of the decade three more. Author Leigh Brackett helped with a lot of his early SF work in the '40s, don't know if she still was in the '50s.