C.O.
N.:
A four year old can understand a lot of things. Tell her the truth.
Mommy is going to a Dr and i will be away for two weeks. Daddy will be bringing you to see me on this date. We will talk every day on the phone (if that's a promise you can keep).
Your son - keep it as simple as possible, much like for your daughter.
In the meantime - if they can tell you are sick - if that's the case - then reassure them that when they see you next that you will be on the road to recovery! YAHOO!
I hope things go well for you.
Best regards,
Cheryl