We had already dropped DD off at the childminders and I was driving with DS to drop him off at this nursery when he brought up the subject of his Dad going into hospital. I was straight with him and told him in simple terms what was happening and how long he would be gone for.
He has just been through it all with me being in hospital so knows that people get better etc.
He burst into hysterical sobs and I about crashed the car. 
So I've brought him to my mum and dads and we are spending the day together.
Nursery shouldnt mind, but i'm not sure what to say to them on the phone! If I say he's ill he'll show me up tomorrow and tell them he wasnt!