I remember some things from under 4

I remember crying because my parents had to give me a puffer for some reason. Running around the house screaming in fear until one of them caught me and forced this very scarylooking thing over my face for me to breath in.

Or I remember dancing with my mother, or cutting my finger (by shutting a door on it no less) and keeping the bandaid on much longer than necessary "to make sure it healed all the way". Helping 'make' mashed potatoes (throw the cut up peices into a pot, very very helpful I was).

Having my parents scream at each other, is a not so nice memory. Or the big hole in the door that my dad punched through. Not that he'd ever hit us, just the door.

Oh and I remember sneaking into the kitchen with my siblings and saying "i'm not scared of lightning" and then screaming like the little girl I was when another bolt struck.

That's why you should always be careful what you do with children, you never know what exactly they'll remember. So try to be nice in all your interactions, and if you make a mistake apologize. I'm sure they'll remember that, and if they don't they'll still have positive feelings for you.