When a brother and sister learn why their grandfather davens every day they realize he is not as boring as they thought. Spoiler: He prays because he promised to do so if his daughter (their mother) did not die. He also promised G-d to stop gambling. Immigrant life on the Lower East Side of New York is briefly covered. I find the whole idea of making deals with G-d problematic, but one of the teachers in my school loves the book and reads this to her 4th grade class every year.

Draft of message to 4th grade teacher (not sent):
Grandpa's Gamble is a problematic book,
but as Eric A. Kimmel, noted children's author, said about his book, Gershon's Monster,

"Gershon's Monster is a disturbing story. It's supposed to be. Those are the
ones you remember. They shake you up. Do children suffer for their parents'
shortcomings? Absolutely! That's what keeps psychiatrists in business."

I think, if you want to use Grandpa's Gamble, you should ask a lot of questions and let the children talk about it;
i.e., it needs lots of discussion.
In the past, apparently some children have felt that if they do good deeds or give money for Tzedakah,
then their relatives will be cured.
And if they are not cured, then --- well there is no good outcome to that:
Either the children failed somehow to "do good" correctly or their relatives don't deserve to get better or
G-d doesn't listen to prayers or G-d chose not to help them or there is no G-d.
I remember an adult friend dying of cancer who became even more depressed
because she tried the positive imaging that was supposed to make her better
and, when she got worse, blamed herself for not trying successfully.

Here are some additional thoughts about Grandpa's Gamble:

I like the illustrations (by Barry Moser, who has illustrated many magnificent books)
and the fact that not only is the method of drawing explained,
but also the origins of the paper.
Moser's description of the paper makes me think that he found the story worthy of its use.

The book is more about the struggles of immigrants
than it is about the power of prayer.
It is more about children seeing old people as boring
than it is about the beauty of piety.
It is more a story about t'shuvah and becoming a better person
than it is about one prayer to save the life of an innocent child.
I suppose that the reason you want to use this book is that it is a lesson in T'shuvah.

Perhaps the grandfather changes because his daughter's miraculous cure
makes him realize---maybe for the first time in his life of hardship---
that sometimes good things actually happen honestly
(random acts of kindness, in this case, by G-d)
and that the values he had---such as, acquiring money is good even if it is gotten unethically---are not the ones he should have.
Perhaps he did not believe in G-d or felt he had no need of G-d before his daughter got sick
and her illness made him reach out---"there are no atheists in foxholes"
and her cure made him rejoice and see the world in a different, better, more positive way.
(He seems to be a man of extremes.)

The story is meant to provoke questions and discussion:
Do you know what your grandparents were like as young adults?
Do you agree with the grandmother, who says that G-d is too busy with his plans to listen to prayers,
or with grandfather, who stubbornly prays for a needed miracle?
What is the first method the grandfather uses to make his daughter well?
How many doctors does he see?
Why do we pray?
Do you ever pray to get something?
Why do we spend so much time teaching how to pray?
Do we believe G-d hears our prayers?
Does he answer them?
Did G-d heal the girl?
Would she have gotten better anyway?
If G-d can heal the girl, then did he make her sick first?
Why would he do that?
To make the grandfather repent?
Is that a good reason?
Are the sins of the fathers visited on the children?
How does this story compare with Gershon's Monster,
a fantasy where the sins of the father literally attack the children?
(An even better book in my opinion.)
What if we don't believe in G-d?
Did the grandfather believe in G-d before his daughter got sick? After?
Does praying still make any sense if you don't believe in G-d?
Can we use the act of prayer as a way to think about what is important to us
and what we should be doing with our lives?
What would the grandfather have done if his daughter had not gotten better?
What would you have done if you were the grandfather?
How much did the grandmother know? Would you have married the grandfather?
Would you have learned the skill that your cousin wanted to teach you---
as was frequently done with newer immigrants---
even if that skill was cheating at cards?
How does he feel about his parents' decision to send him away to America?
Is he happy about it or angry with them?
Is the grandfather a good man?
What does he think of himself? What do you think of him?
What did he do with his ill-gotten gains when he decides to go straight?
Where did your family come from?
Do you know what their lives were like when they first came to the United States?
Before they came here?
How does the grandfather's history parallel the Exodus story and Passover?
(The events take place on erev Pesach and I think that the parallel stories are significant for the author.)
Did you notice that there seems to be a siddur on the floor? Did it bother you?
Why does the grandfather spend all day long davvening?
Or does it only seem that way to children?
Shouldn't he be doing other things as well?
Why does the children's mother tell them to be quiet?
Why should he be shown respect?
Is he religious? What does it mean to be religious?
Do you think he is observant in any other way besides davvening?
Why did the grandchildren not know about his story before?
What message is the author trying to share?
Do you agree with it?
Do you realize that it is perfectly OK to disagree?
Do you know that just because something is written down, it is not necessarily "true"?

These questions were off the top of my head
and in not a lot of order.
There are more.
This book is not evil and unacceptable.
It presents a point of view and maybe even more than one.
It is worth reading and enjoying.
It is not perfect; the ending is a bit forced and cute.
The grandfather is not completely admirable, by any means.
But it has more depth than many a children's book with exactly one moral.

Perhaps I have too much faith in the intelligence of 4th graders;
I think they can handle the questions above.

I think that your point of view and way of life are valuable things for children to see.
It is obvious to them that there are other ways of being Jewish besides what you demonstrate---
their own lives tell them that.
I also think it is important that just as your way of being Jewish should be acceptable to them,
their way of being Jewish must be acceptable to you. ( )