I used cloth on my kids and covered with the "plastic pants". I found them very convenient - running low on diapers? - do a load of wash! Much easier than constantly dragging home huge boxes of product and then carrying the same quantity (plus a little more!) to the garbage. As a bonus, I have all of these cotton diapers to use as nice soft cloths yet today.
My kids are fully grown now and I don't have any grandchildren yet. My daughter will use eco-friendly products so would be thrilled with a gift like yours. My son - hmmm - what will my future daughter-in-law do?
I agree with all that folks said above. The parents will know if that is the way they want to go. And, if it is what they want they will be thrilled that you are offering to make them for them!
Please let us know what happens!