I don't have a problem with Isabella's hair. It looks fine to me, and as others have said, she was probably running around and playing with the other children so it's natural that her hair would look a little messier than usual. I agree that Isabella looks a lot like Frederik. I think Christian has the same "mannerisms" (not sure if this is the correct word to use here) and posture as Frederik, though facially I think he looks more like Mary. He has her eyes IMO.
"For beautiful eyes, look for the good in others; for beautiful lips, speak only words of kindness; and for poise, walk with the knowledge that you are never alone". Audrey Hepburn
"Think of all the beauty still left around you and be happy". Anne Frank