I'd hand regular height cabinets and use a step stool (or look at the pull out style cabinetry). We do have a shorter toilet (not too short but shorter than I prefer) for the kids. It was inexpensive and the contractor said it could easily be swapped with a larger model when it is outgrown.

I agree with the others, I wouldn't change your entire bathroom to fit your kids right now. There are plenty of options to be make more kid user that can also be used by other (or as they grow). Like the hide away step that comes out from the bottom of the bathroom vanity.