Who sold you the kickboat oars????
You should NEVER have been given a set of those diameter oars on a 12' boat. You should only have been supplied the standard diameter oars. I didn't realize they made the smaller diameter oars in an 8 1/2-9' length (which you should be using on a 12' boat). I'd go back to whoever it was that sold you those and tell them you want some sort of refund and/or upgrade free (minus any cost difference) to the correct oars. It was probably too much pressure that broke them. The amount of pressure vs. boat size/weight would automatically cause too much flex on them. Those smaller diameter sizes are meant for 9' and under sized boats ONLY! I had a set for my old 9' Steelheader and eventually sold them off and used my spare set of 8' full sized cataracts on it. Worked great.
It isn't the oars, more then likely it was the overkill (like trying to land a 50# king on a 3wt), you can do it but won't be pretty or dependable.
"Good angling ethic is not a monopoly practiced just by fly fisherman" - Bill McMillan