Don't want to engage in any battle, however I will somewhat reluctantly give my .02 cents in case anyone deems my opinion / contribution of any value.
As it relates to ice - I am not a fan, there is way too many reviews and articles (many posted here already) that indicate no value unless of actual injury, and may (likely) inhibits recovery as a post throwing protocol.
Marc Pro (sp?) - I spent time with Kyle (Driveline) in Nashville recently, and have read or studied the device, and do believe there is some definite benefit of using, specifically for post throwing recovery / and or rehab.
As any of this relates to 12 year old, I am not sure of any value....if a 12 year old is needing post throwing arm care, or experiencing arm soreness, I think something else is in play here. Most studies show that micro tears, or potential danger to ligaments, or tendons exist primarily for those throwing in excess of 80 MPH or more, and the harder you throw the higher the risk.