Dressing Oneself

I lose track of what kids should be doing at what age...esp. when it comes to comparing Maddie & Will to Katie & Alex. I was very surprised last week when I saw Maddie put on her own pants and her coat all by herself. I know that the older girls weren't doing that at 2, but I don't know if this is comon for other 2 year olds or not. Maddie is also my undresser. Most naps we will find her in a diaper or naked (if she has figured out how to undo the tape that I had to place around her diaper!). We were shocked one morning to find her still dressed - only to realize that her shirt was inside out and backwards and the pants were also inside out! At that point we realized that she knew how to dress herself.