Whoops, 5 year old. That rules out the Feynman Lectures (free online).
So, I think that kids are most likely to be fascinated and engaged with real gizmo's. I started with little electrical gadgets. Forgot if I ever got a motor to spin.
There are some fun experiments at IOP.
https://www.iop.org/explore-physics
Experiments do require supervision. Physics is a human activity.
Another thing that got me excited was just looking at stars. That got me into astronomy and astrophysics. (and optics and optical engineering).
One cool app I got my daughter was "Gizmos and Gadgets", a simulation app that was fun to hack around with. It's long gone. You might see if the free and open source gcompris has anything of interest to your youngster.
Has binaries for everything, including RaspberryPi 3.
https://gcompris.net/index-en.html
GCompris is a high quality educational software suite, including a large number of activities for children aged 2 to 10.
Some of the activities are game orientated, but nonetheless still educational.
Here is the list of activity categories with some examples:
• computer discovery: keyboard, mouse, touchscreen ...
• reading: letters, words, reading practice, typing text ...
• arithmetic: numbers, operations, table memory, enumeration, double entry table ...
• science: the canal lock, the water cycle, renewable energy ...
• geography: countries, regions, culture ...
• games: chess, memory, align 4, hangman, tic-tac-toe ...
• other: colors, shapes, Braille, learn to tell time ...
Currently GCompris offers more than 100 activities, and more are being developed. GCompris is free software, it means that you can adapt it to your own needs, improve it, and most importantly share it with children everywhere.
It's a wonderful experience to further the natural curiosity of a child. I loved every minute of it.
Thermodynamics
Richard Feynman's dad guided him in observing the natural world and asking "why do you think that bird behaves the way it does?" (and variations on that theme); rather than asking what the bird is called, ask what it's doing and why.
I would avoid abstraction layers. Keep it grounded in observational reality as they build their motor skills.
I'm a licensed high school physics teacher and parent of a six year old. My approach has been similar with the high school students; anchor learning in the observable world, appealing to as many senses as possible.