T.
I am so sorry to hear about your Dog's illness.
We just put our 15 year old American Eskimo to sleep a few weeks ago due to kidney failure.
Our daughter is just 17 months old, so she really doesn't have any concept of where Taz is. But we do have 4 cats and another dog, so her attention is on the ones that are here. It is harder on my husband and I than on her.
As a little girl, I do remember that our German Sheppard Fuffy was hit by a car on a Sunday morning as church was letting out. I was 2.5 at the time and to this day I can remember her on our front porch with the bloody leg and my Dad taking her to the Dr's. My parents never told me that she had to be put down. I was too young to understand it all anyway. They told me she was in the hospital and she couldn't come home. I always believed that and I remember from time to time asking for her, until one day I realized that she must have died and that was just something they told me not to upset me. I didn't get all upset about it and certainly didn't get mad at anyone for "Not telling me the truth". I just accepted it.
I am in no way suggesting that you not tell your 4 year old the truth, but I do believe that children take things a lot better than we think they will. My parent's always thought that once I found out about Fluffy, I would fall apart, but I didn't and I was ok with it all.
If you can explain that she is very sick and that God will be taking her soon to live with him so that she will not be sick again, I think your child will be ok with that. I know there is always the thought to replace a pet with another, but that will be too soon for you and your husband also. Let a little time go by before you think about replacing your pet.
You will all need time to grieve and to heal.
Children do have to face death in some way at some point in their young lives. I do believe dealing with the loss of a pet is a better experience than (God forbid) a family member. It will be the first of many experiences with dealth unfortunately, but as long as your children have you and your husband to guide them and support them, they will handle it well.
My best to you T..
I know how heavy your heart is and I know the desire you have to protect your little one's hearts.
P.S. I did have a cat with cancer. She was too far gone when they decided to give her the prednisone so I didn't see any help with it, but your experiences may be different. The prednisone with make your dog pretty thirsty and she will have to pee a lot more than usual also. She may have a few accidents in the house too b/c of it. Sometimes dealing with the side effects of the medications can be tougher than dealing with the disease itself.
Saying prayers for all of you and for the comfort of your "First child". We know that feeling too!
Take care,
P.