Literature available on resistance training for ages 9-14?

Does anyone know of any literature available that discourages resistant training in younger age groups? Two of my sons are swimming for a local club and the coach wants my 10 year old to use a drag suit and paddles. Before I confront the coach on this issue I need some literature that suggests resistant training in pre-puberty individuals is misquided. Does anyone know of any articles suggesting younger age groups should use more technique related drills instead of power driven sets? I need evidence against this practice to show the coach and other parents. My opinion isn't enough. I have a couple of Go Swim articles and articles off of the USA Swimming site, but I feel I need more. Thanks for any response.