My 4 year old started playing and he loves it, I didn't expect him liking it so much so soon. He now wants to play every day. I started a peaceful mode game for him and joined in multiplayer. He was just running around to learn the controls and explore, mining trees in the start, but eventually, he started to copy basic smelting setups and now he plays with construction robots and copy pastes solar arays.
I'm actually quite suprised how well the game scales as the technology goes on. Small/unexperienced kids can do super simple things like running around/mining random stuff and exploring, and then, they can step by step do more and more sophisticated things and explore the game as they age and/or get more experienced and the the technologies unlock.
Next game, we will play without peaceful mode.