If your son is four now, I doubt he has more than a couple more years with the speech impediment. I don’t think it’s worth changing the pronunciation for. Mountain out of molehill, kind of.
That being said, I think both ways are beautiful, but the soft TH version will require less correcting, at least in English speaking countries. (The only “[name_u]TAY[/name_u]-uh” I know is spelled [name_f]Tea[/name_f] with an accent over the E, which is annoying for her because official US legal documents, like driver’s license and insurance cards, don’t recognize accented letters and it looks like her name is just [name_f]Tea[/name_f], like the drink.)