Mine take most of Monday to get back in routine. They aren't so much a problem as much as I have learned just to have a looser structure on Monday in terms of what I plan for them so I can pick and choose from activities according to moods and tiredness. Naptime is usually longer as they make up for a busy weekend. I find by Friday they are often the same and either need to be left alone to play or totally told what to do with me led stuff. I now plan my lessons to be T, W, Th and we play M and F by ear.