coach4kids

I'm the head coach of 8-11 year olds, tackle team. I have a OC and a DC, here is where my questions come in. as a head coach what abilities do I have/ what are my limits as far as calling plays. I gave my coaches the choice to run what ever offense and defense they wanted with the statement of if it is not working I will ask you to change it. Well we have hit that point a couple of times this season, and when I have asked to run a play it is not done. And then when I question why, I'm told "it wont work"
So by now you can see where the problem is. Am I way out of bounds for stepping in and trying to get things back on track? Should I let them make all the decisions and just field question from the parents?

Thank you for your input
coach4kids