Baking soda and lots of water then use the leather conditioner after. The leather conditioner is just making the leather more porous and letting it absorb the vomit moisture in. Also check really good in the seat crevices and seat belts. It sounds really gross but puke tends to sneak in everywhere. I'm thanking The Lord my 5 year old has only chucked in my wife's car.
2010 335i MSport / 2011 535i / 2014 435i M Sport