Slide to aviod collision

[BlueMan86]

9-12yo rec ball, we use ASA rules with some rec and parks adjustments, in our rules it states
"All players must slide or avoid collision with a defensive player if a play is being made on that player at a particular base. If the player does not slide or attempt to avoid collision, she will be called out."
The way I see it is that if the runner makes any sort of contact with the fielder while a play is being made it is an out. Basically to avoid interference and physical harm.
Well there is a coach in the league who insists that his girls do not know how to slide and can hurt themselves if they try to. (I really want to tell him to take his girls on the grass and teach them how to slide, but I think it will be overstepping my bounds).
This past weekend, said coach came up to me and told me he is not going to have his girls slide, I replied that if there is a play and they do not slide it will be an out. On one play I heard him tell a runner rounding third to run through the plate, it was not a close play but that leads to my question, if there was some sort of collision, what would you do with the coach?
I hope this made sense.