Suggestions for building an Amazon Fire tablet for child

[Android Central Question]

I have an Amazon Fire (5th gen) 7" which my child has been using for a couple of years under the 'Fire for Kids'/Freetime gui. I want to rebuild it to clean out the detritus that collects over time and was wondering if there's a way to give it a more grown up (std) look but still retain control over apps and time limits.
I've tried using third party apps such as Screen time and DinnerTime Plus in the past, but they don't play well with the Amazon ecosystem.
Does anyone have experience in doing this or any suggestions?