I'm not the original person asking about playing by ear. But I've been taking all the advice so far, playing kids songs and stuff. My question is how do you know what key you're currently playing in. Like, I start one of the songs on the note C, play for a bit, and find that there's a Bb. Then I'm like, "Oh. I'm playing in F not C. Gotta restart a fourth down on G."
i guess just start with songs where it's really obvious. and then get a feel for what it means. then you will be able to figure other songs out. although i don't know, i've never had trouble with it, and i know many adults who still assume songs are in the key of the first chord, even when it seems obvious to me that that's not really the key. i don't really know why some people get this easily and others don't. it's kind of like seeing a house and knowing whether you are looking at it from the side or the front. i don't know how to really explain that to someone