I think I need more information to be able to answer this.
If the group of newbies has no experiencing role-playing at all, then the Red Box might be a good thing for them to start with, especially if one of them is going to be running the game. But it will only be useful for the intro game, after that you'll need some other products to keep playing.
If, on the other hand, you are planning to DM the game for the new players, I'd say that the Red Box is less useful. You clearly have experience with 3.5, so you know how RPGs work in general, and you just need to kit yourself out to be able to handle 4e. In that case, I'd recommend getting a copy of the Rules Compendium, and either Heroes of the Forgotten Kingdoms or Heroes of the Fallen Lands or both. Depending on your budget, and whether or not you already own other 4e books, you might also want to get the Monster Vault.
If your budget is limited, then the Dungeon Master's Kit might be worthwhile looking at. It's a mediocre product if you already have the Rules Compendium, and even moreso if you already have the 4e Dungeon Master's Guide. But if you have neither of those, the Kit isn't a bad way to get most of the rules, some good DMing advice, a bunch of encounters, a two-part adventure, two poster maps and a DM screen.