Heya, I think I've been able to accomplish exactly what your trying to do... but I'm creating the matrix children automatically during the parent items aftersubmit event, and specifically adding the values that need to be set. Would that work for you? If not, I'm working on another item where in the beforesubmit event, certain fields are calculated etc. and defaults could be set at that point as well... however I haven't gotten that to work during matrix child creation yet. I'm not 100% certain that the matrix item creation wizard triggers the beforesubmit event, and not even sure that it is triggered when a matrix item is created initially (through the api). I know it works on manual save of the item. If you came up with a solution, I'd love to hear it... otherwise, when I figure it out I'll share.