Ahhh kids are such perceptive things. As someone else put it, I think they know things are changing but don't know exactly what and how to deal with it. I think it might be a combination of that plus the tiredness making it worse... Definitely agree that keeping the routines as normal as possible will help them get back into the swing of normal life. But not overdoing it.

I know when DD comes home from kinder on Friday afternoon, all she wants to do is lie on the couch - end of the week, tired, Friday is a big day, so I just let her. By Saturday, after a good sleep, she is usually back to her bright self. Might take a bit more TLC with your two.

Don't forget to go easy on yourself too.