HI< I think having the sleep issues checked sounds like a good idea. I have not had any expierence with this, but have you tried to really counter his mood. I mean everyone walking around with a clown nose on, or just being silly, funny. It sounds like he has the power over everyone, he is Mr Grump, and so everyone follows his lead. At four he should be able to understand role play, and if everyone takes on a different role, being silly, and not being upset by his grumpiness, perhaps the Mr grump will have to go play somewhere else. Just a thought, Marie.