Hi J.,
Oh, your little one probably heard "Oh my God" at the daycare and it just takes one time and they can mimic it for quite awhile.
I'm a Christian, a pastor's wife and a mother of ten children -- 25 down to 4. So we've had our rounds with words that weren't good to repeat in a swearing or ill-meaninged way.
Since you've tried verbally to correct it and your son doesn't understand...maybe just the attention he's gotten causes him to continue saying it. So I'd just not comment for a week or so...when he gets no reaction either positive or negative thus no extra attention; maybe he'll just drop it because it's not generating anything from anyone any more.
Plus, singing good Christian songs to or with him, playing good children's Christian cassettes or CD's can put things more in perspective and within one or two playings he'll pickup the words himself more and more. It's important in the long haul to get him into a good Gospel-preaching church...not some denomination that preaches good-works saves you or baptism saves you or things that Jesus didn't teach. Good old John 3:16 is a long verse, but kids learn it when it's repeated and explained to them...if you'd like to see what I consider the best explanation of how a person becomes a Christian. My husband wrote a tract on what Jesus said in John 3:3 "Except a man be born again, he CANNOT see the kingdom of God." That tells me it's important to know what He meant by being born again...anyway my husband explains it well in our church website at www.gospelcenter.us and click on "Born Again" on the top right hand cornered area for the full tract.
Don't you think someone who is a Christian (which is what you become when you're Born Again) but so many say they are but have no interest in gathering regularly with believers in a local church, or reading/studying their Bible to know the Lord better and better (like we know people via their letters to us many times). Truly spiritual life puts desires in a person for these things....to be spiritually dead is seen when there's no desire for any Bible influences on a regular basis. Yet so many say they are Christians, but never gather with believers, read their BIble, pray, etc. I'm concerned....had an excellent message on "false gospels" by my husband's preacher friend this past Tuesday night at our regular weeknight Bible study in our church. If you'd like a copy, I can send you one...interested?
B. in Eau Claire, WI