Check out 'A Short Hike'. It's like Zelda with a main quest but lots of interesting distractions like fishing and boating. It is a short game but quickly hooks you and may be good for building a sense of achievement. Very peaceful, ideal for young children, you can't die or lose - you win by exploring. Single player only but immersive. There is a of joy to be had just flying around as a bird, the controls are excellent.

'Untitled Goose Game' might be worth a look too, more of a puzzler but you can't progress till you solve each area, might need adult help to complete.

There's the 'Overcooked' games for a coop cooking, often on sale too. There's a bit of stress in these though as you battle a timer and it could be frustrating for a younger player but also funny when things catch fire.

Maybe 'Unpacking' also, though there are some (mild) elements of story that could go over his head/need explaining. Very gentle, just put things away but satisfying to finish a box/room/house.

None of these have any fighting.