Is it possible to put them in day care before she leaves, and have her stop by the daycare on her lunch, or pick them up from school one day, and you pick them up the next, for about a week or two until she stops and you are the only one picking them up? Of course they will miss her in their way, but the are young enough that they will get caught up in the excitement and newness of daycare and it won't allow them to think to much about it. Children deal with loss much better than we as adults do. They grow attached to teachers, friends, even children they don't know at a park for a couple of hours, and then these people can be taken out of their lives without warning. You could also keep a picture of them in the house or in their room, but I personally feel that this may prolong the sadness especially if they will not be seeing her again.
Give them a little extra attention, do some things different around the house, maybe in their room, bright new sheets or curtains, a new paint job, a new painting in their room. I'm not sure if they are speaking yet, or if they will be asking for her, but mostly their reaction will be in their behaviors. Likely a little more cranky, and little more rebellious, a little more whiny, but after a while they will feel better, with a lot of love and a little more affection than normal. Just don't allow the crankiness to get out of hand where their taking advantage of you feeling sorry for them, even at that young age they can see where to gain a foothold into getting their own way. I think they will be fine.
I welcome your thoughts, let me know if you want to talk more.