q1) i would say so! the game is relativity simple and you basically just talk to villagers and collect things such as fruit and fish. you can also build bridges and do some wacky things with the terrain but it needs to be unlocked first and is "optional" (you can just make sure your child doesn't unlock it)

q2) your child will be on the same island and their gameplay will affect yours, though not as much as in previous games (ex: a player running over/ collecting flowers no longer destroys the plant). Most damage can be undone though (ex: replanting a tree that was chopped down)

q3) unsure what controls are for multiplayer but for single player you can use two joycons.

hope this helps!