Actually both Alix and May were known to be happy little creatures, always laughing and making others laugh. It was only later that smile got lost from Alix´s face. To judge something like that from a photograph doesn´t really make much sense. They were little children, probably told to just hold still, and had to endure the long and tiring photography process with poses changing and everyting. If I was four years old like May, I too wouldn´t like it. Everybody in that time looks depressed in the photos, simply because it was kind of a fashion and to look expresionless (or "Sad") doesn´t make your muscles hurt like trying to keep up your smile for minutes.