My (now) five year old started out playing a few games I had on the PC. Very simply indie games that you just kind of felt out the movement. There was this fantastic little game where you navigate around a world full of brightly coloured bouncing balloons that she absolutely adored.
Then when she was a bit older she moved onto Donut County on the Switch. She absolutely adores that one, to the point that she's beaten it on her own. I recommend that to every parent who asks.