3yo hair falling out

So...I was washing Spock's hair and I noticed she had what looked like cradle cap, was like a crusty scab like thing on her head, I started picking it off, and with it her hair was coming out with it, in clumps! As soon as I worked out what was happening I stopped. But now she has a 2 x 2 cm bald patch on top of her head! Like bald bald, like I'm really concerned there is no more hair even going to grow there. And she has more of these scab like things too.....
What the hell could it be?? Now I think back I have seen similar clumps of hair around the house, but I honestly thought they were the cats. =(
Help please thanks.

DD1 is 8.5 and had cradle cap up until a few years ago, hers came out in clumps too if I picked the scabs so I just left it. Might pay to get her checked by GP though incase xxx