A.,
I know it is hard because they do not understand fully. We have had to explain several different deaths to our son. With another one soon (his aunt). We explain to him that she/he has gone on to a better place and is watching over him to keep him safe throughout the day. We explain that they love him very much but he will not be able to hug or talk to he/she like he is used to. However, whenever he is sad and wants the person, he can just talk to them and they will hear him, just not answer back. However, while u still have them around, if your mom is up to it, let her call mamaw, anytime of the week during this time. You could even possibly see if the hospital will let her come see her mamaw (if she is close enough), at least once, so she can tell her bye. Just be honest with her. Some believe it is not appropriate to let the kids go to viewings/layouts, and/or funerals. However, we have always taken our son. It does not seem to phase him. We tried with the first one when he was actually able to walk, to keep him out in the waiting area, but when he saw, everyone in the other room, he wanted to know what was going on, he went in, saw his great-great aunt laying in the casket, waved to her, and then walked around to talk to everyone.
There is no real answer. It just depends on what works for you and your family. My niece, is going through this right now with her 4 year old (it's her mom, that we know is going die soon).
Hope it helps,
T.