11 year old legal pitch from wind-up

[Rbn3]

Several pitchers I have witnessed this year plant their free foot sideways toward first (in the case of rhps). Some even plant their free foot in front of the rubber as a "rocker step". Rules say "backward" and "forward" only steps allowed with free foot. Some umps have said they can't see it when pointed out - so I drop it. Other's say they know the rule but they don't enforce it since "these kids are just learning to pitch." I guess my belief is that this is the exact reason why it should be enforced so they don't develop bad mechanics. What is the custom on how to deal with this. And how do umps judge what is "backwards," i.e. is moving the foot behind the rubber all that is needed, even if the step is basically "backing up" towards first base?