George, you are not 'Off Topic' this is a Technics instrument forum which is not confined to the KN series. Quite a few of the members have the PR series pianos.
I have heard the PR604 and it's big brother the PR804 and was VERY impressed with the sounds and facilities on these instruments. One feature which may be of particular interest to you, since you mentioned that your children would use it to learn, is the inclusion of the 'Progessive Pianist' training facility on the PR804. It is certainly worth looking at but not knowing what your budget is, the 804 may be a bit expensive.
Welcome to the Forum George



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Willum