mpv sftp://192.168.1.123:/home/remote-user/Films/Peppa_Pig_Against_Gerrymandering.mkv
I used a very basic floating window manager and created about 6 or 10 large desktop icons to run the things I had installed for him (Hyperspace Delivery Boy was a favorite 8-)
One icon started a script which launched the media player in a specific directory.
I highly recommend giving (very young) kids exposure to a wide variety of desktop user interfaces. Failure to do this has led to an entire generation (2 or 3?) of windoze based computer illiteracy.
Computers really aren't all about right-clicking that thing that looks like a pineapple, then selecting Settings, etc...
In fact I maintain one of those setups mentioned by TFA with some neighbours (lots of tech people/artists with rare media in the neighborhood for reasons), and friends and family in other countries.
The whole point of most of these setups (for people with family), is to be safe, simple, efficient, and low-maintenance for the whole family to be able to enjoy media.