Well, this is embarrassing. I just caught my 4 year old fiddling herself down there. It doesn't look like she's deliberately trying to find any sexual pleasure, more like she's just touching her vag like it's normal. Do kids her age do this? Should I worry?

I would not worry. It's totally normal. Even infants do that. Not all, but it's common. Boys and girls both do it. However you can explain to her, that these are sensitive areas. And should not touch. Our hands have germs on them. It's not intentional. Don't worry