Strike zone questions

[gvsulife]

Is a ball considered a strike where it crosses the front of the plate? Does the rule book stay anything about this? or does the strike zone changed based on where the batter is standing in the box?

I remember being taught back in the day that a strike or ball is determined from where the ball crosses the front of the plate?.?.

My problem is when kids are moving up to the top of the box and the ball is high from where they are standing but it crosses the plate in the strike zone. this is mostly a result of some extremely slow pitching. However, even with off speed stuff that sinks or drops I have struggling to be consistent. I don't know what the ruling is! So hopefully somebody can help provide some clarification or shed some light on my situation.

Thank you in advance!