Now, at 6, we have resumed piano lessons. She is responsible for practice, her emotions, and her progress. It is SO much easier. We changed methods so she has one or two songs to learn each week, and once she demonstrates competency, she moves on. Practice is no more than 20 minutes. We are all happy with this arrangement.
That's what we are doing with DS6. He has at most 5 short songs to practice and he does all that on his own. I don't even have to remind him to practice. DS4 too has at most 5 short pieces (right now he has 3) but we need to make sure he practices which I admit is always not easy. 2 weeks ago his teacher let him pick up any song he wanted to learn. I thought that was very nice and motivating.
MoN your previous arrangement with 1+ hour practicing sounded way too much for a small child. Even as an adult I wouldn't want to play something over and over again. I am glad she was able to resume lessons now.